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Date: Wed, 28 Jun 2017 10:11:12 -0500
From: Josh Poimboeuf <jpoimboe@...hat.com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>, Jiri Slaby <jslaby@...e.cz>,
Ingo Molnar <mingo@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v2 8/8] x86/unwind: add undwarf unwinder
Add a new 'undwarf' unwinder which is enabled by
CONFIG_UNDWARF_UNWINDER. It plugs into the existing x86 unwinder
framework.
It relies on objtool to generate the needed .undwarf section.
For more details on why undwarf is used instead of DWARF, see
tools/objtool/Documentation/undwarf.txt.
Thanks to Andy Lutomirski for the performance improvement ideas:
splitting the undwarf table into two parallel arrays and creating a fast
lookup table to search a subset of the undwarf table.
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
Documentation/x86/undwarf.txt | 146 ++++++++++
arch/um/include/asm/unwind.h | 8 +
arch/x86/Kconfig | 1 +
arch/x86/Kconfig.debug | 25 ++
arch/x86/include/asm/module.h | 9 +
arch/x86/include/asm/unwind.h | 77 +++--
arch/x86/kernel/Makefile | 8 +-
arch/x86/kernel/module.c | 12 +-
arch/x86/kernel/setup.c | 3 +
arch/x86/kernel/unwind_frame.c | 39 ++-
arch/x86/kernel/unwind_guess.c | 5 +
arch/x86/kernel/unwind_undwarf.c | 589 ++++++++++++++++++++++++++++++++++++++
arch/x86/kernel/vmlinux.lds.S | 2 +
include/asm-generic/vmlinux.lds.h | 20 +-
lib/Kconfig.debug | 3 +
scripts/Makefile.build | 14 +-
16 files changed, 898 insertions(+), 63 deletions(-)
create mode 100644 Documentation/x86/undwarf.txt
create mode 100644 arch/um/include/asm/unwind.h
create mode 100644 arch/x86/kernel/unwind_undwarf.c
diff --git a/Documentation/x86/undwarf.txt b/Documentation/x86/undwarf.txt
new file mode 100644
index 0000000..d76c6b4
--- /dev/null
+++ b/Documentation/x86/undwarf.txt
@@ -0,0 +1,146 @@
+Undwarf unwinder debuginfo generation
+=====================================
+
+Overview
+--------
+
+The kernel CONFIG_UNDWARF_UNWINDER option enables objtool generation of
+undwarf debuginfo, which is out-of-band data which is used by the
+in-kernel undwarf unwinder. It's similar in concept to DWARF CFI
+debuginfo which would be used by a DWARF unwinder. The difference is
+that the format of the undwarf data is simpler than DWARF, which in turn
+allows the unwinder to be simpler and faster.
+
+Objtool generates the undwarf data by first doing compile-time stack
+metadata validation (CONFIG_STACK_VALIDATION). After analyzing all the
+code paths of a .o file, it determines information about the stack state
+at each instruction address in the file and outputs that information to
+the .undwarf and .undwarf_ip sections.
+
+The undwarf sections are combined at link time and are sorted at boot
+time. The unwinder uses the resulting data to correlate instruction
+addresses with their stack states at run time.
+
+
+Undwarf vs frame pointers
+-------------------------
+
+With frame pointers enabled, GCC adds instrumentation code to every
+function in the kernel. The kernel's .text size increases by about
+3.2%, resulting in a broad kernel-wide slowdown. Measurements by Mel
+Gorman [1] have shown a slowdown of 5-10% for some workloads.
+
+In contrast, the undwarf unwinder has no effect on text size or runtime
+performance, because the debuginfo is out of band. So if you disable
+frame pointers and enable undwarf, you get a nice performance
+improvement across the board, and still have reliable stack traces.
+
+Another benefit of undwarf compared to frame pointers is that it can
+reliably unwind across interrupts and exceptions. Frame pointer based
+unwinds can skip the caller of the interrupted function if it was a leaf
+function or if the interrupt hit before the frame pointer was saved.
+
+The main disadvantage of undwarf compared to frame pointers is that it
+needs more memory to store the undwarf table: roughly 2-4MB depending on
+the kernel config.
+
+
+Undwarf vs DWARF
+----------------
+
+Undwarf debuginfo's advantage over DWARF itself is that it's much
+simpler. It gets rid of the complex DWARF CFI state machine and also
+gets rid of the tracking of unnecessary registers. This allows the
+unwinder to be much simpler, meaning fewer bugs, which is especially
+important for mission critical oops code.
+
+The simpler debuginfo format also enables the unwinder to be much faster
+than DWARF, which is important for perf and lockdep. In a basic
+performance test by Jiri Slaby [2], the undwarf unwinder was about 20x
+faster than an out-of-tree DWARF unwinder. (Note: that measurement was
+taken before some performance tweaks were implemented, so the speedup
+may be even higher.)
+
+The undwarf format does have a few downsides compared to DWARF. The
+undwarf table takes up ~2MB more memory than an DWARF .eh_frame table.
+
+Another potential downside is that, as GCC evolves, it's conceivable
+that the undwarf data may end up being *too* simple to describe the
+state of the stack for certain optimizations. But IMO this is unlikely
+because GCC saves the frame pointer for any unusual stack adjustments it
+does, so I suspect we'll really only ever need to keep track of the
+stack pointer and the frame pointer between call frames. But even if we
+do end up having to track all the registers DWARF tracks, at least we
+will still be able to control the format, e.g. no complex state
+machines.
+
+
+Undwarf debuginfo generation
+----------------------------
+
+The undwarf data is generated by objtool. With the existing
+compile-time stack metadata validation feature, objtool already follows
+all code paths, and so it already has all the information it needs to be
+able to generate undwarf data from scratch. So it's an easy step to go
+from stack validation to undwarf generation.
+
+It should be possible to instead generate the undwarf data with a simple
+tool which converts DWARF to undwarf. However, such a solution would be
+incomplete due to the kernel's extensive use of asm, inline asm, and
+special sections like exception tables.
+
+That could be rectified by manually annotating those special code paths
+using GNU assembler .cfi annotations in .S files, and homegrown
+annotations for inline asm in .c files. But asm annotations were tried
+in the past and were found to be unmaintainable. They were often
+incorrect/incomplete and made the code harder to read and keep updated.
+And based on looking at glibc code, annotating inline asm in .c files
+might be even worse.
+
+Objtool still needs a few annotations, but only in code which does
+unusual things to the stack like entry code. And even then, far fewer
+annotations are needed than what DWARF would need, so they're much more
+maintainable than DWARF CFI annotations.
+
+So the advantages of using objtool to generate undwarf are that it gives
+more accurate debuginfo, with very few annotations. It also insulates
+the kernel from toolchain bugs which can be very painful to deal with in
+the kernel since we often have to workaround issues in older versions of
+the toolchain for years.
+
+The downside is that the unwinder now becomes dependent on objtool's
+ability to reverse engineer GCC code paths. If GCC optimizations become
+too complicated for objtool to follow, the undwarf generation might stop
+working or become incomplete. (It's worth noting that livepatch already
+has such a dependency on objtool's ability to follow GCC code paths.)
+
+If newer versions of GCC come up with some optimizations which break
+objtool, we may need to revisit the current implementation. Some
+possible solutions would be asking GCC to make the optimizations more
+palatable, or having objtool use DWARF as an additional input, or
+creating a GCC plugin to assist objtool with its analysis. But for now,
+objtool follows GCC code quite well.
+
+
+Unwinder implementation details
+-------------------------------
+
+Objtool generates the undwarf data by integrating with the compile-time
+stack metadata validation feature, which is described in detail in
+tools/objtool/Documentation/stack-validation.txt. After analyzing all
+the code paths of a .o file, it creates an array of undwarf structs, and
+a parallel array of instruction addresses associated with those structs,
+and writes them to the .undwarf and .undwarf_ip sections respectively.
+
+The undwarf data is split into the two arrays for performance reasons,
+to make the searchable part of the data (.undwarf_ip) more compact. The
+arrays are sorted in parallel at boot time.
+
+Performance is further improved by the use of a fast lookup table which
+is created at runtime. The fast lookup table associates a given address
+with a range of undwarf table indices, so that only a small subset of
+the undwarf table needs to be searched.
+
+
+[1] https://lkml.kernel.org/r/20170602104048.jkkzssljsompjdwy@suse.de
+[2] https://lkml.kernel.org/r/d2ca5435-6386-29b8-db87-7f227c2b713a@suse.cz
diff --git a/arch/um/include/asm/unwind.h b/arch/um/include/asm/unwind.h
new file mode 100644
index 0000000..53f507c
--- /dev/null
+++ b/arch/um/include/asm/unwind.h
@@ -0,0 +1,8 @@
+#ifndef _ASM_UML_UNWIND_H
+#define _ASM_UML_UNWIND_H
+
+static inline void
+unwind_module_init(struct module *mod, void *undwarf_ip, size_t unward_ip_size,
+ void *undwarf, size_t undwarf_size) {}
+
+#endif /* _ASM_UML_UNWIND_H */
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 72028a1..adf3222 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -153,6 +153,7 @@ config X86
select HAVE_MEMBLOCK
select HAVE_MEMBLOCK_NODE_MAP
select HAVE_MIXED_BREAKPOINTS_REGS
+ select HAVE_MOD_ARCH_SPECIFIC
select HAVE_NMI
select HAVE_OPROFILE
select HAVE_OPTPROBES
diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index fcb7604..995434c 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -357,4 +357,29 @@ config PUNIT_ATOM_DEBUG
The current power state can be read from
/sys/kernel/debug/punit_atom/dev_power_state
+config UNDWARF_UNWINDER
+ bool "undwarf unwinder"
+ depends on X86_64
+ select STACK_VALIDATION
+ ---help---
+ This option enables the "undwarf" unwinder for unwinding kernel stack
+ traces. It uses a custom data format which is a simplified version
+ of the DWARF Call Frame Information standard.
+
+ This unwinder is more accurate across interrupt entry frames than the
+ frame pointer unwinder. This also can enable a small performance
+ improvement across the entire kernel if CONFIG_FRAME_POINTER is
+ disabled.
+
+ Enabling this option will increase the kernel's runtime memory usage
+ by roughly 2-4MB, depending on your kernel config.
+
+config FRAME_POINTER_UNWINDER
+ def_bool y
+ depends on !UNDWARF_UNWINDER && FRAME_POINTER
+
+config GUESS_UNWINDER
+ def_bool y
+ depends on !UNDWARF_UNWINDER && !FRAME_POINTER
+
endmenu
diff --git a/arch/x86/include/asm/module.h b/arch/x86/include/asm/module.h
index e3b7819..4dc6427 100644
--- a/arch/x86/include/asm/module.h
+++ b/arch/x86/include/asm/module.h
@@ -2,6 +2,15 @@
#define _ASM_X86_MODULE_H
#include <asm-generic/module.h>
+#include <asm/undwarf.h>
+
+struct mod_arch_specific {
+#ifdef CONFIG_UNDWARF_UNWINDER
+ unsigned int num_undwarves;
+ int *undwarf_ip;
+ struct undwarf *undwarf;
+#endif
+};
#ifdef CONFIG_X86_64
/* X86_64 does not define MODULE_PROC_FAMILY */
diff --git a/arch/x86/include/asm/unwind.h b/arch/x86/include/asm/unwind.h
index e667649..1f8cb78 100644
--- a/arch/x86/include/asm/unwind.h
+++ b/arch/x86/include/asm/unwind.h
@@ -12,11 +12,14 @@ struct unwind_state {
struct task_struct *task;
int graph_idx;
bool error;
-#ifdef CONFIG_FRAME_POINTER
+#if defined(CONFIG_UNDWARF_UNWINDER)
+ bool signal, full_regs;
+ unsigned long sp, bp, ip;
+ struct pt_regs *regs;
+#elif defined(CONFIG_FRAME_POINTER)
bool got_irq;
- unsigned long *bp, *orig_sp;
+ unsigned long *bp, *orig_sp, ip;
struct pt_regs *regs;
- unsigned long ip;
#else
unsigned long *sp;
#endif
@@ -24,41 +27,30 @@ struct unwind_state {
void __unwind_start(struct unwind_state *state, struct task_struct *task,
struct pt_regs *regs, unsigned long *first_frame);
-
bool unwind_next_frame(struct unwind_state *state);
-
unsigned long unwind_get_return_address(struct unwind_state *state);
+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state);
static inline bool unwind_done(struct unwind_state *state)
{
return state->stack_info.type == STACK_TYPE_UNKNOWN;
}
-static inline
-void unwind_start(struct unwind_state *state, struct task_struct *task,
- struct pt_regs *regs, unsigned long *first_frame)
-{
- first_frame = first_frame ? : get_stack_pointer(task, regs);
-
- __unwind_start(state, task, regs, first_frame);
-}
-
static inline bool unwind_error(struct unwind_state *state)
{
return state->error;
}
-#ifdef CONFIG_FRAME_POINTER
-
static inline
-unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+void unwind_start(struct unwind_state *state, struct task_struct *task,
+ struct pt_regs *regs, unsigned long *first_frame)
{
- if (unwind_done(state))
- return NULL;
+ first_frame = first_frame ? : get_stack_pointer(task, regs);
- return state->regs ? &state->regs->ip : state->bp + 1;
+ __unwind_start(state, task, regs, first_frame);
}
+#if defined(CONFIG_UNDWARF_UNWINDER) || defined(CONFIG_FRAME_POINTER)
static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
{
if (unwind_done(state))
@@ -66,20 +58,47 @@ static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
return state->regs;
}
-
-#else /* !CONFIG_FRAME_POINTER */
-
-static inline
-unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+#else
+static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
{
return NULL;
}
+#endif
-static inline struct pt_regs *unwind_get_entry_regs(struct unwind_state *state)
+#ifdef CONFIG_UNDWARF_UNWINDER
+void unwind_init(void);
+void unwind_module_init(struct module *mod, void *undwarf_ip,
+ size_t undwarf_ip_size, void *undwarf,
+ size_t undwarf_size);
+#else
+static inline void unwind_init(void) {}
+static inline void unwind_module_init(struct module *mod, void *undwarf_ip,
+ size_t undwarf_ip_size, void *undwarf,
+ size_t undwarf_size) {}
+#endif
+
+/*
+ * This disables KASAN checking when reading a value from another task's stack,
+ * since the other task could be running on another CPU and could have poisoned
+ * the stack in the meantime.
+ */
+#define READ_ONCE_TASK_STACK(task, x) \
+({ \
+ unsigned long val; \
+ if (task == current) \
+ val = READ_ONCE(x); \
+ else \
+ val = READ_ONCE_NOCHECK(x); \
+ val; \
+})
+
+static inline bool task_on_another_cpu(struct task_struct *task)
{
- return NULL;
+#ifdef CONFIG_SMP
+ return task != current && task->on_cpu;
+#else
+ return false;
+#endif
}
-#endif /* CONFIG_FRAME_POINTER */
-
#endif /* _ASM_X86_UNWIND_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 3c7c419..4865889 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -125,11 +125,9 @@ obj-$(CONFIG_PERF_EVENTS) += perf_regs.o
obj-$(CONFIG_TRACING) += tracepoint.o
obj-$(CONFIG_SCHED_MC_PRIO) += itmt.o
-ifdef CONFIG_FRAME_POINTER
-obj-y += unwind_frame.o
-else
-obj-y += unwind_guess.o
-endif
+obj-$(CONFIG_UNDWARF_UNWINDER) += unwind_undwarf.o
+obj-$(CONFIG_FRAME_POINTER_UNWINDER) += unwind_frame.o
+obj-$(CONFIG_GUESS_UNWINDER) += unwind_guess.o
###
# 64 bit specific files
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index f67bd32..203b5a7 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -35,6 +35,7 @@
#include <asm/page.h>
#include <asm/pgtable.h>
#include <asm/setup.h>
+#include <asm/unwind.h>
#if 0
#define DEBUGP(fmt, ...) \
@@ -213,7 +214,7 @@ int module_finalize(const Elf_Ehdr *hdr,
struct module *me)
{
const Elf_Shdr *s, *text = NULL, *alt = NULL, *locks = NULL,
- *para = NULL;
+ *para = NULL, *undwarf = NULL, *undwarf_ip = NULL;
char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
for (s = sechdrs; s < sechdrs + hdr->e_shnum; s++) {
@@ -225,6 +226,10 @@ int module_finalize(const Elf_Ehdr *hdr,
locks = s;
if (!strcmp(".parainstructions", secstrings + s->sh_name))
para = s;
+ if (!strcmp(".undwarf", secstrings + s->sh_name))
+ undwarf = s;
+ if (!strcmp(".undwarf_ip", secstrings + s->sh_name))
+ undwarf_ip = s;
}
if (alt) {
@@ -248,6 +253,11 @@ int module_finalize(const Elf_Ehdr *hdr,
/* make jump label nops */
jump_label_apply_nops(me);
+ if (undwarf && undwarf_ip)
+ unwind_module_init(me, (void *)undwarf_ip->sh_addr,
+ undwarf_ip->sh_size,
+ (void *)undwarf->sh_addr, undwarf->sh_size);
+
return 0;
}
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 65622f0..d736761 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -115,6 +115,7 @@
#include <asm/microcode.h>
#include <asm/mmu_context.h>
#include <asm/kaslr.h>
+#include <asm/unwind.h>
/*
* max_low_pfn_mapped: highest direct mapped pfn under 4GB
@@ -1303,6 +1304,8 @@ void __init setup_arch(char **cmdline_p)
if (efi_enabled(EFI_BOOT))
efi_apply_memmap_quirks();
#endif
+
+ unwind_init();
}
#ifdef CONFIG_X86_32
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index b9389d7..7574ef5 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -10,20 +10,22 @@
#define FRAME_HEADER_SIZE (sizeof(long) * 2)
-/*
- * This disables KASAN checking when reading a value from another task's stack,
- * since the other task could be running on another CPU and could have poisoned
- * the stack in the meantime.
- */
-#define READ_ONCE_TASK_STACK(task, x) \
-({ \
- unsigned long val; \
- if (task == current) \
- val = READ_ONCE(x); \
- else \
- val = READ_ONCE_NOCHECK(x); \
- val; \
-})
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+ if (unwind_done(state))
+ return 0;
+
+ return __kernel_text_address(state->ip) ? state->ip : 0;
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+{
+ if (unwind_done(state))
+ return NULL;
+
+ return state->regs ? &state->regs->ip : state->bp + 1;
+}
static void unwind_dump(struct unwind_state *state)
{
@@ -66,15 +68,6 @@ static void unwind_dump(struct unwind_state *state)
}
}
-unsigned long unwind_get_return_address(struct unwind_state *state)
-{
- if (unwind_done(state))
- return 0;
-
- return __kernel_text_address(state->ip) ? state->ip : 0;
-}
-EXPORT_SYMBOL_GPL(unwind_get_return_address);
-
static size_t regs_size(struct pt_regs *regs)
{
/* x86_32 regs from kernel mode are two words shorter: */
diff --git a/arch/x86/kernel/unwind_guess.c b/arch/x86/kernel/unwind_guess.c
index 039f367..4f0e17b 100644
--- a/arch/x86/kernel/unwind_guess.c
+++ b/arch/x86/kernel/unwind_guess.c
@@ -19,6 +19,11 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);
+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+{
+ return NULL;
+}
+
bool unwind_next_frame(struct unwind_state *state)
{
struct stack_info *info = &state->stack_info;
diff --git a/arch/x86/kernel/unwind_undwarf.c b/arch/x86/kernel/unwind_undwarf.c
new file mode 100644
index 0000000..44f62af
--- /dev/null
+++ b/arch/x86/kernel/unwind_undwarf.c
@@ -0,0 +1,589 @@
+#include <linux/module.h>
+#include <linux/sort.h>
+#include <asm/ptrace.h>
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+#include <asm/undwarf.h>
+#include <asm/sections.h>
+
+#define undwarf_warn(fmt, ...) \
+ printk_deferred_once(KERN_WARNING pr_fmt("WARNING: " fmt), ##__VA_ARGS__)
+
+extern int __start_undwarf_ip[];
+extern int __stop_undwarf_ip[];
+extern struct undwarf __start_undwarf[];
+extern struct undwarf __stop_undwarf[];
+
+bool undwarf_init;
+static DEFINE_MUTEX(sort_mutex);
+
+int *cur_undwarf_ip_table = __start_undwarf_ip;
+struct undwarf *cur_undwarf_table = __start_undwarf;
+
+/*
+ * This is a lookup table for speeding up access to the undwarf table. Given
+ * an input address offset, the corresponding lookup table entry specifies a
+ * subset of the undwarf table to search.
+ *
+ * Each block represents the end of the previous range and the start of the
+ * next range. An extra block is added to give the last range an end.
+ *
+ * Some measured performance results for different values of LOOKUP_NUM_BLOCKS:
+ *
+ * num blocks array size lookup speedup total speedup
+ * 2k 8k 1.5x 1.5x
+ * 4k 16k 1.6x 1.6x
+ * 8k 32k 1.8x 1.7x
+ * 16k 64k 2.0x 1.8x
+ * 32k 128k 2.5x 2.0x
+ * 64k 256k 2.9x 2.2x
+ * 128k 512k 3.3x 2.4x
+ *
+ * Go with 32k blocks because it doubles unwinder performance while only adding
+ * 3.5% to the undwarf data footprint.
+ */
+#define LOOKUP_NUM_BLOCKS (32 * 1024)
+static unsigned int undwarf_fast_lookup[LOOKUP_NUM_BLOCKS + 1] __ro_after_init;
+
+#define LOOKUP_START_IP (unsigned long)_stext
+#define LOOKUP_STOP_IP (unsigned long)_etext
+#define LOOKUP_BLOCK_SIZE \
+ (DIV_ROUND_UP(LOOKUP_STOP_IP - LOOKUP_START_IP, \
+ LOOKUP_NUM_BLOCKS))
+
+
+static inline unsigned long undwarf_ip(const int *ip)
+{
+ return (unsigned long)ip + *ip;
+}
+
+static struct undwarf *__undwarf_find(int *ip_table, struct undwarf *u_table,
+ unsigned int num_entries,
+ unsigned long ip)
+{
+ int *first = ip_table;
+ int *last = ip_table + num_entries - 1;
+ int *mid = first, *found = first;
+
+ if (!num_entries)
+ return NULL;
+
+ /*
+ * Do a binary range search to find the rightmost duplicate of a given
+ * starting address. Some entries are section terminators which are
+ * "weak" entries for ensuring there are no gaps. They should be
+ * ignored when they conflict with a real entry.
+ */
+ while (first <= last) {
+ mid = first + ((last - first) / 2);
+
+ if (undwarf_ip(mid) <= ip) {
+ found = mid;
+ first = mid + 1;
+ } else
+ last = mid - 1;
+ }
+
+ return u_table + (found - ip_table);
+}
+
+static struct undwarf *undwarf_find(unsigned long ip)
+{
+ struct module *mod;
+
+ if (!undwarf_init)
+ return NULL;
+
+ /* For non-init vmlinux addresses, use the fast lookup table: */
+ if (ip >= LOOKUP_START_IP && ip < LOOKUP_STOP_IP) {
+ unsigned int idx, start, stop;
+
+ idx = (ip - LOOKUP_START_IP) / LOOKUP_BLOCK_SIZE;
+
+ if (WARN_ON_ONCE(idx >= LOOKUP_NUM_BLOCKS))
+ return NULL;
+
+ start = undwarf_fast_lookup[idx];
+ stop = undwarf_fast_lookup[idx + 1] + 1;
+
+ if (WARN_ON_ONCE(__start_undwarf + start >= __stop_undwarf) ||
+ __start_undwarf + stop > __stop_undwarf)
+ return NULL;
+
+ return __undwarf_find(__start_undwarf_ip + start,
+ __start_undwarf + start,
+ stop - start, ip);
+ }
+
+ /* vmlinux .init slow lookup: */
+ if (ip >= (unsigned long)_sinittext && ip < (unsigned long)_einittext)
+ return __undwarf_find(__start_undwarf_ip, __start_undwarf,
+ __stop_undwarf - __start_undwarf, ip);
+
+ /* Module lookup: */
+ mod = __module_address(ip);
+ if (!mod || !mod->arch.undwarf || !mod->arch.undwarf_ip)
+ return NULL;
+ return __undwarf_find(mod->arch.undwarf_ip, mod->arch.undwarf,
+ mod->arch.num_undwarves, ip);
+}
+
+static void undwarf_sort_swap(void *_a, void *_b, int size)
+{
+ struct undwarf *undwarf_a, *undwarf_b;
+ struct undwarf undwarf_tmp;
+ int *a = _a, *b = _b, tmp;
+ int delta = _b - _a;
+
+ /* Swap the undwarf_ip entries: */
+ tmp = *a;
+ *a = *b + delta;
+ *b = tmp - delta;
+
+ /* Swap the corresponding undwarf entries: */
+ undwarf_a = cur_undwarf_table + (a - cur_undwarf_ip_table);
+ undwarf_b = cur_undwarf_table + (b - cur_undwarf_ip_table);
+ undwarf_tmp = *undwarf_a;
+ *undwarf_a = *undwarf_b;
+ *undwarf_b = undwarf_tmp;
+}
+
+static int undwarf_sort_cmp(const void *_a, const void *_b)
+{
+ struct undwarf *undwarf_a;
+ const int *a = _a, *b = _b;
+ unsigned long a_val = undwarf_ip(a);
+ unsigned long b_val = undwarf_ip(b);
+
+ if (a_val > b_val)
+ return 1;
+ if (a_val < b_val)
+ return -1;
+
+ /*
+ * The "weak" section terminator entries need to always be on the left
+ * to ensure the lookup code skips them in favor of real entries.
+ * These terminator entries exist to handle any gaps created by
+ * whitelisted .o files which didn't get objtool generation.
+ */
+ undwarf_a = cur_undwarf_table + (a - cur_undwarf_ip_table);
+ return undwarf_a->cfa_reg == UNDWARF_REG_UNDEFINED ? -1 : 1;
+}
+
+void unwind_module_init(struct module *mod, void *_undwarf_ip,
+ size_t undwarf_ip_size, void *_undwarf,
+ size_t undwarf_size)
+{
+ int *undwarf_ip = _undwarf_ip;
+ struct undwarf *undwarf = _undwarf;
+ unsigned int num_entries = undwarf_ip_size / sizeof(int);
+
+ WARN_ON_ONCE(undwarf_ip_size % sizeof(int) != 0 ||
+ undwarf_size % sizeof(*undwarf) != 0 ||
+ num_entries != undwarf_size / sizeof(*undwarf));
+
+ /*
+ * The 'cur_undwarf_*' globals allow the undwarf_sort_swap() callback
+ * to associate an undwarf_ip table entry with its corresponding
+ * undwarf entry so they can both be swapped.
+ */
+ mutex_lock(&sort_mutex);
+ cur_undwarf_ip_table = undwarf_ip;
+ cur_undwarf_table = undwarf;
+ sort(undwarf_ip, num_entries, sizeof(int),undwarf_sort_cmp,
+ undwarf_sort_swap);
+ mutex_unlock(&sort_mutex);
+
+ mod->arch.undwarf_ip = undwarf_ip;
+ mod->arch.undwarf = undwarf;
+ mod->arch.num_undwarves = num_entries;
+}
+
+void __init unwind_init(void)
+{
+ size_t undwarf_ip_size = (void *)__stop_undwarf_ip - (void *)__start_undwarf_ip;
+ size_t undwarf_size = (void *)__stop_undwarf - (void *)__start_undwarf;
+ size_t num_entries = undwarf_ip_size / sizeof(int);
+ struct undwarf *undwarf;
+ int i;
+
+ if (!num_entries || undwarf_ip_size % sizeof(int) != 0 ||
+ undwarf_size % sizeof(struct undwarf) != 0 ||
+ num_entries != undwarf_size / sizeof(struct undwarf)) {
+ pr_warn("WARNING: Bad or missing undwarf table. Disabling unwinder.\n");
+ return;
+ }
+
+ /* Sort the undwarf table: */
+ sort(__start_undwarf_ip, num_entries, sizeof(int), undwarf_sort_cmp,
+ undwarf_sort_swap);
+
+ /* Initialize the fast lookup table: */
+ for (i = 0; i < LOOKUP_NUM_BLOCKS; i++) {
+ undwarf = __undwarf_find(__start_undwarf_ip, __start_undwarf,
+ num_entries,
+ LOOKUP_START_IP + (LOOKUP_BLOCK_SIZE * i));
+ if (!undwarf) {
+ pr_warn("WARNING: Corrupt undwarf table. Disabling unwinder.\n");
+ return;
+ }
+
+ undwarf_fast_lookup[i] = undwarf - __start_undwarf;
+ }
+
+ /* Initialize the last 'end' block: */
+ undwarf = __undwarf_find(__start_undwarf_ip, __start_undwarf,
+ num_entries, LOOKUP_STOP_IP);
+ if (!undwarf) {
+ pr_warn("WARNING: Corrupt undwarf table. Disabling unwinder.\n");
+ return;
+ }
+ undwarf_fast_lookup[LOOKUP_NUM_BLOCKS] = undwarf - __start_undwarf;
+
+ undwarf_init = true;
+}
+
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+ if (unwind_done(state))
+ return 0;
+
+ return __kernel_text_address(state->ip) ? state->ip : 0;
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
+unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
+{
+ if (unwind_done(state))
+ return NULL;
+
+ if (state->regs)
+ return &state->regs->ip;
+
+ if (state->sp)
+ return (unsigned long *)state->sp - 1;
+
+ return NULL;
+}
+
+static bool stack_access_ok(struct unwind_state *state, unsigned long addr,
+ size_t len)
+{
+ struct stack_info *info = &state->stack_info;
+
+ /*
+ * If the address isn't on the current stack, switch to the next one.
+ *
+ * We may have to traverse multiple stacks to deal with the possibility
+ * that info->next_sp could point to an empty stack and the address
+ * could be on a subsequent stack.
+ */
+ while (!on_stack(info, (void *)addr, len))
+ if (get_stack_info(info->next_sp, state->task, info,
+ &state->stack_mask))
+ return false;
+
+ return true;
+}
+
+static bool deref_stack_reg(struct unwind_state *state, unsigned long addr,
+ unsigned long *val)
+{
+ if (!stack_access_ok(state, addr, sizeof(long)))
+ return false;
+
+ *val = READ_ONCE_TASK_STACK(state->task, *(unsigned long *)addr);
+ return true;
+}
+
+#define REGS_SIZE (sizeof(struct pt_regs))
+#define SP_OFFSET (offsetof(struct pt_regs, sp))
+#define IRET_REGS_SIZE (REGS_SIZE - offsetof(struct pt_regs, ip))
+#define IRET_SP_OFFSET (SP_OFFSET - offsetof(struct pt_regs, ip))
+
+static bool deref_stack_regs(struct unwind_state *state, unsigned long addr,
+ unsigned long *ip, unsigned long *sp, bool full)
+{
+ size_t regs_size = full ? REGS_SIZE : IRET_REGS_SIZE;
+ size_t sp_offset = full ? SP_OFFSET : IRET_SP_OFFSET;
+ struct pt_regs *regs = (struct pt_regs *)(addr + regs_size - REGS_SIZE);
+
+ if (IS_ENABLED(CONFIG_X86_64)) {
+ if (!stack_access_ok(state, addr, regs_size))
+ return false;
+
+ *ip = regs->ip;
+ *sp = regs->sp;
+
+ return true;
+ }
+
+ if (!stack_access_ok(state, addr, sp_offset))
+ return false;
+
+ *ip = regs->ip;
+
+ if (user_mode(regs)) {
+ if (!stack_access_ok(state, addr + sp_offset,
+ REGS_SIZE - SP_OFFSET))
+ return false;
+
+ *sp = regs->sp;
+ } else
+ *sp = (unsigned long)®s->sp;
+
+ return true;
+}
+
+bool unwind_next_frame(struct unwind_state *state)
+{
+ enum stack_type prev_type = state->stack_info.type;
+ unsigned long ip_p, prev_sp = state->sp;
+ unsigned long cfa, orig_ip, orig_sp;
+ struct undwarf *undwarf;
+ struct pt_regs *ptregs;
+ bool indirect = false;
+
+ if (unwind_done(state))
+ return false;
+
+ /* Don't let modules unload while we're reading their undwarf data. */
+ preempt_disable();
+
+ /* Have we reached the end? */
+ if (state->regs && user_mode(state->regs))
+ goto done;
+
+ /*
+ * Find the undwarf table entry associated with the text address.
+ *
+ * Decrement call return addresses by one so they work for sibling
+ * calls and calls to noreturn functions.
+ */
+ undwarf = undwarf_find(state->signal ? state->ip : state->ip - 1);
+ if (!undwarf || undwarf->cfa_reg == UNDWARF_REG_UNDEFINED)
+ goto done;
+ orig_ip = state->ip;
+
+ /* Calculate the CFA (caller frame address): */
+ switch (undwarf->cfa_reg) {
+ case UNDWARF_REG_SP:
+ cfa = state->sp + undwarf->cfa_offset;
+ break;
+
+ case UNDWARF_REG_BP:
+ cfa = state->bp + undwarf->cfa_offset;
+ break;
+
+ case UNDWARF_REG_SP_INDIRECT:
+ cfa = state->sp + undwarf->cfa_offset;
+ indirect = true;
+ break;
+
+ case UNDWARF_REG_BP_INDIRECT:
+ cfa = state->bp + undwarf->cfa_offset;
+ indirect = true;
+ break;
+
+ case UNDWARF_REG_R10:
+ if (!state->regs || !state->full_regs) {
+ undwarf_warn("missing regs for base reg R10 at ip %p\n",
+ (void *)state->ip);
+ goto done;
+ }
+ cfa = state->regs->r10;
+ break;
+
+ case UNDWARF_REG_R13:
+ if (!state->regs || !state->full_regs) {
+ undwarf_warn("missing regs for base reg R13 at ip %p\n",
+ (void *)state->ip);
+ goto done;
+ }
+ cfa = state->regs->r13;
+ break;
+
+ case UNDWARF_REG_DI:
+ if (!state->regs || !state->full_regs) {
+ undwarf_warn("missing regs for base reg DI at ip %p\n",
+ (void *)state->ip);
+ goto done;
+ }
+ cfa = state->regs->di;
+ break;
+
+ case UNDWARF_REG_DX:
+ if (!state->regs || !state->full_regs) {
+ undwarf_warn("missing regs for base reg DX at ip %p\n",
+ (void *)state->ip);
+ goto done;
+ }
+ cfa = state->regs->dx;
+ break;
+
+ default:
+ undwarf_warn("unknown CFA base reg %d for ip %p\n",
+ undwarf->cfa_reg, (void *)state->ip);
+ goto done;
+ }
+
+ if (indirect) {
+ if (!deref_stack_reg(state, cfa, &cfa))
+ goto done;
+ }
+
+ /* Find IP, SP and possibly regs: */
+ switch (undwarf->type) {
+ case UNDWARF_TYPE_CFA:
+ ip_p = cfa - sizeof(long);
+
+ if (!deref_stack_reg(state, ip_p, &state->ip))
+ goto done;
+
+ state->ip = ftrace_graph_ret_addr(state->task, &state->graph_idx,
+ state->ip, (void *)ip_p);
+
+ state->sp = cfa;
+ state->regs = NULL;
+ state->signal = false;
+ break;
+
+ case UNDWARF_TYPE_REGS:
+ if (!deref_stack_regs(state, cfa, &state->ip, &state->sp, true)) {
+ undwarf_warn("can't dereference registers at %p for ip %p\n",
+ (void *)cfa, (void *)orig_ip);
+ goto done;
+ }
+
+ state->regs = (struct pt_regs *)cfa;
+ state->full_regs = true;
+ state->signal = true;
+ break;
+
+ case UNDWARF_TYPE_REGS_IRET:
+ orig_sp = state->sp;
+ if (!deref_stack_regs(state, cfa, &state->ip, &state->sp, false)) {
+ undwarf_warn("can't dereference iret registers at %p for ip %p\n",
+ (void *)cfa, (void *)orig_ip);
+ goto done;
+ }
+
+ ptregs = container_of((void *)cfa, struct pt_regs, ip);
+ if ((unsigned long)ptregs >= orig_sp &&
+ on_stack(&state->stack_info, ptregs, REGS_SIZE)) {
+ state->regs = ptregs;
+ state->full_regs = false;
+ } else
+ state->regs = NULL;
+
+ state->signal = true;
+ break;
+
+ default:
+ undwarf_warn("unknown undwarf type %d\n", undwarf->type);
+ break;
+ }
+
+ /* Find BP: */
+ switch (undwarf->bp_reg) {
+ case UNDWARF_REG_UNDEFINED:
+ if (state->regs && state->full_regs)
+ state->bp = state->regs->bp;
+ break;
+
+ case UNDWARF_REG_CFA:
+ if (!deref_stack_reg(state, cfa + undwarf->bp_offset,&state->bp))
+ goto done;
+ break;
+
+ case UNDWARF_REG_BP:
+ if (!deref_stack_reg(state, state->bp + undwarf->bp_offset, &state->bp))
+ goto done;
+ break;
+
+ default:
+ undwarf_warn("unknown BP base reg %d for ip %p\n",
+ undwarf->bp_reg, (void *)orig_ip);
+ goto done;
+ }
+
+ /* Prevent a recursive loop due to bad undwarf data: */
+ if (state->stack_info.type == prev_type &&
+ on_stack(&state->stack_info, (void *)state->sp, sizeof(long)) &&
+ state->sp <= prev_sp) {
+ undwarf_warn("stack going in the wrong direction? ip=%p\n",
+ (void *)orig_ip);
+ goto done;
+ }
+
+ preempt_enable();
+ return true;
+
+done:
+ preempt_enable();
+ state->stack_info.type = STACK_TYPE_UNKNOWN;
+ return false;
+}
+EXPORT_SYMBOL_GPL(unwind_next_frame);
+
+void __unwind_start(struct unwind_state *state, struct task_struct *task,
+ struct pt_regs *regs, unsigned long *first_frame)
+{
+ memset(state, 0, sizeof(*state));
+ state->task = task;
+
+ /*
+ * Refuse to unwind the stack of a task while it's executing on another
+ * CPU. This check is racy, but that's ok: the unwinder has other
+ * checks to prevent it from going off the rails.
+ */
+ if (task_on_another_cpu(task))
+ goto done;
+
+ if (regs) {
+ if (user_mode(regs))
+ goto done;
+
+ state->ip = regs->ip;
+ state->sp = kernel_stack_pointer(regs);
+ state->bp = regs->bp;
+ state->regs = regs;
+ state->full_regs = true;
+ state->signal = true;
+
+ } else if (task == current) {
+ asm volatile("lea (%%rip), %0\n\t"
+ "mov %%rsp, %1\n\t"
+ "mov %%rbp, %2\n\t"
+ : "=r" (state->ip), "=r" (state->sp),
+ "=r" (state->bp));
+
+ } else {
+ struct inactive_task_frame *frame = (void *)task->thread.sp;
+
+ state->ip = frame->ret_addr;
+ state->sp = task->thread.sp;
+ state->bp = frame->bp;
+ }
+
+ if (get_stack_info((unsigned long *)state->sp, state->task,
+ &state->stack_info, &state->stack_mask))
+ return;
+
+ /*
+ * The caller can provide the address of the first frame directly
+ * (first_frame) or indirectly (regs->sp) to indicate which stack frame
+ * to start unwinding at. Skip ahead until we reach it.
+ */
+ while (!unwind_done(state) &&
+ (!on_stack(&state->stack_info, first_frame, sizeof(long)) ||
+ state->sp <= (unsigned long)first_frame))
+ unwind_next_frame(state);
+
+ return;
+
+done:
+ state->stack_info.type = STACK_TYPE_UNKNOWN;
+ return;
+}
+EXPORT_SYMBOL_GPL(__unwind_start);
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index c8a3b61..e3b7cfc 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -148,6 +148,8 @@ SECTIONS
BUG_TABLE
+ UNDWARF_TABLE
+
. = ALIGN(PAGE_SIZE);
__vvar_page = .;
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 0d64658..a8ed616 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -668,6 +668,24 @@
#define BUG_TABLE
#endif
+#ifdef CONFIG_UNDWARF_UNWINDER
+#define UNDWARF_TABLE \
+ . = ALIGN(4); \
+ .undwarf_ip : AT(ADDR(.undwarf_ip) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__start_undwarf_ip) = .; \
+ KEEP(*(.undwarf_ip)) \
+ VMLINUX_SYMBOL(__stop_undwarf_ip) = .; \
+ } \
+ . = ALIGN(8); \
+ .undwarf : AT(ADDR(.undwarf) - LOAD_OFFSET) { \
+ VMLINUX_SYMBOL(__start_undwarf) = .; \
+ KEEP(*(.undwarf)) \
+ VMLINUX_SYMBOL(__stop_undwarf) = .; \
+ }
+#else
+#define UNDWARF_TABLE
+#endif
+
#ifdef CONFIG_PM_TRACE
#define TRACEDATA \
. = ALIGN(4); \
@@ -854,7 +872,7 @@
DATA_DATA \
CONSTRUCTORS \
} \
- BUG_TABLE
+ BUG_TABLE \
#define INIT_TEXT_SECTION(inittext_align) \
. = ALIGN(inittext_align); \
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9c5d40a..ec79366 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -374,6 +374,9 @@ config STACK_VALIDATION
pointers (if CONFIG_FRAME_POINTER is enabled). This helps ensure
that runtime stack traces are more reliable.
+ This is also a prerequisite for creation of the undwarf format which
+ is needed for CONFIG_UNDWARF_UNWINDER.
+
For more information, see
tools/objtool/Documentation/stack-validation.txt.
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 733e044..7859c79 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -258,7 +258,8 @@ ifneq ($(SKIP_STACK_VALIDATION),1)
__objtool_obj := $(objtree)/tools/objtool/objtool
-objtool_args = check
+objtool_args = $(if $(CONFIG_UNDWARF_UNWINDER),undwarf generate,check)
+
ifndef CONFIG_FRAME_POINTER
objtool_args += --no-fp
endif
@@ -276,6 +277,11 @@ objtool_obj = $(if $(patsubst y%,, \
endif # SKIP_STACK_VALIDATION
endif # CONFIG_STACK_VALIDATION
+# Rebuild all objects when objtool changes, or is enabled/disabled.
+objtool_dep = $(objtool_obj) \
+ $(wildcard include/config/undwarf/unwinder.h \
+ include/config/stack/validation.h)
+
define rule_cc_o_c
$(call echo-cmd,checksrc) $(cmd_checksrc) \
$(call cmd_and_fixdep,cc_o_c) \
@@ -298,13 +304,13 @@ cmd_undef_syms = echo
endif
# Built-in and composite module parts
-$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_obj) FORCE
+$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
$(call cmd,force_checksrc)
$(call if_changed_rule,cc_o_c)
# Single-part modules are special since we need to mark them in $(MODVERDIR)
-$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_obj) FORCE
+$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
$(call cmd,force_checksrc)
$(call if_changed_rule,cc_o_c)
@{ echo $(@:.o=.ko); echo $@; \
@@ -399,7 +405,7 @@ cmd_modversions_S = \
endif
endif
-$(obj)/%.o: $(src)/%.S $(objtool_obj) FORCE
+$(obj)/%.o: $(src)/%.S $(objtool_dep) FORCE
$(call if_changed_rule,as_o_S)
targets += $(real-objs-y) $(real-objs-m) $(lib-y)
--
2.7.5
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