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Message-Id: <20210812190603.25326-5-madvenka@linux.microsoft.com>
Date: Thu, 12 Aug 2021 14:06:03 -0500
From: madvenka@...ux.microsoft.com
To: mark.rutland@....com, broonie@...nel.org, jpoimboe@...hat.com,
ardb@...nel.org, nobuta.keiya@...itsu.com,
sjitindarsingh@...il.com, catalin.marinas@....com, will@...nel.org,
jmorris@...ei.org, pasha.tatashin@...een.com, jthierry@...hat.com,
linux-arm-kernel@...ts.infradead.org,
live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
madvenka@...ux.microsoft.com
Subject: [RFC PATCH v8 4/4] arm64: Create a list of SYM_CODE functions, check return PC against list
From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
SYM_CODE functions don't follow the usual calling conventions. Check if the
return PC in a stack frame falls in any of these. If it does, consider the
stack trace unreliable.
Define a special section for unreliable functions
=================================================
Define a SYM_CODE_END() macro for arm64 that adds the function address
range to a new section called "sym_code_functions".
Linker file
===========
Include the "sym_code_functions" section under read-only data in
vmlinux.lds.S.
Initialization
==============
Define an early_initcall() to create a sym_code_functions[] array from
the linker data.
Unwinder check
==============
Add a reliability check in unwind_is_reliable() that compares a return
PC with sym_code_functions[]. If there is a match, then return failure.
Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
---
arch/arm64/include/asm/linkage.h | 12 +++++++
arch/arm64/include/asm/sections.h | 1 +
arch/arm64/kernel/stacktrace.c | 53 +++++++++++++++++++++++++++++++
arch/arm64/kernel/vmlinux.lds.S | 10 ++++++
4 files changed, 76 insertions(+)
diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
index 9906541a6861..616bad74e297 100644
--- a/arch/arm64/include/asm/linkage.h
+++ b/arch/arm64/include/asm/linkage.h
@@ -68,4 +68,16 @@
SYM_FUNC_END_ALIAS(x); \
SYM_FUNC_END_ALIAS(__pi_##x)
+/*
+ * Record the address range of each SYM_CODE function in a struct code_range
+ * in a special section.
+ */
+#define SYM_CODE_END(name) \
+ SYM_END(name, SYM_T_NONE) ;\
+ 99: ;\
+ .pushsection "sym_code_functions", "aw" ;\
+ .quad name ;\
+ .quad 99b ;\
+ .popsection
+
#endif
diff --git a/arch/arm64/include/asm/sections.h b/arch/arm64/include/asm/sections.h
index e4ad9db53af1..c84c71063d6e 100644
--- a/arch/arm64/include/asm/sections.h
+++ b/arch/arm64/include/asm/sections.h
@@ -21,5 +21,6 @@ extern char __exittext_begin[], __exittext_end[];
extern char __irqentry_text_start[], __irqentry_text_end[];
extern char __mmuoff_data_start[], __mmuoff_data_end[];
extern char __entry_tramp_text_start[], __entry_tramp_text_end[];
+extern char __sym_code_functions_start[], __sym_code_functions_end[];
#endif /* __ASM_SECTIONS_H */
diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index b60f8a20ba64..26dbdd4fff77 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -18,6 +18,31 @@
#include <asm/stack_pointer.h>
#include <asm/stacktrace.h>
+struct code_range {
+ unsigned long start;
+ unsigned long end;
+};
+
+static struct code_range *sym_code_functions;
+static int num_sym_code_functions;
+
+int __init init_sym_code_functions(void)
+{
+ size_t size = (unsigned long)__sym_code_functions_end -
+ (unsigned long)__sym_code_functions_start;
+
+ sym_code_functions = (struct code_range *)__sym_code_functions_start;
+ /*
+ * Order it so that sym_code_functions is not visible before
+ * num_sym_code_functions.
+ */
+ smp_mb();
+ num_sym_code_functions = size / sizeof(struct code_range);
+
+ return 0;
+}
+early_initcall(init_sym_code_functions);
+
/*
* AArch64 PCS assigns the frame pointer to x29.
*
@@ -185,6 +210,10 @@ void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
*/
static bool notrace unwind_is_reliable(struct stackframe *frame)
{
+ const struct code_range *range;
+ unsigned long pc;
+ int i;
+
/*
* If the PC is not a known kernel text address, then we cannot
* be sure that a subsequent unwind will be reliable, as we
@@ -192,6 +221,30 @@ static bool notrace unwind_is_reliable(struct stackframe *frame)
*/
if (!__kernel_text_address(frame->pc))
return false;
+
+ /*
+ * Check the return PC against sym_code_functions[]. If there is a
+ * match, then the consider the stack frame unreliable.
+ *
+ * As SYM_CODE functions don't follow the usual calling conventions,
+ * we assume by default that any SYM_CODE function cannot be unwound
+ * reliably.
+ *
+ * Note that this includes:
+ *
+ * - Exception handlers and entry assembly
+ * - Trampoline assembly (e.g., ftrace, kprobes)
+ * - Hypervisor-related assembly
+ * - Hibernation-related assembly
+ * - CPU start-stop, suspend-resume assembly
+ * - Kernel relocation assembly
+ */
+ pc = frame->pc;
+ for (i = 0; i < num_sym_code_functions; i++) {
+ range = &sym_code_functions[i];
+ if (pc >= range->start && pc < range->end)
+ return false;
+ }
return true;
}
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 709d2c433c5e..2bf769f45b54 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -111,6 +111,14 @@ jiffies = jiffies_64;
#define TRAMP_TEXT
#endif
+#define SYM_CODE_FUNCTIONS \
+ . = ALIGN(16); \
+ .symcode : AT(ADDR(.symcode) - LOAD_OFFSET) { \
+ __sym_code_functions_start = .; \
+ KEEP(*(sym_code_functions)) \
+ __sym_code_functions_end = .; \
+ }
+
/*
* The size of the PE/COFF section that covers the kernel image, which
* runs from _stext to _edata, must be a round multiple of the PE/COFF
@@ -196,6 +204,8 @@ SECTIONS
swapper_pg_dir = .;
. += PAGE_SIZE;
+ SYM_CODE_FUNCTIONS
+
. = ALIGN(SEGMENT_ALIGN);
__init_begin = .;
__inittext_begin = .;
--
2.25.1
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