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Message-ID: <20151026180216.GH29592@lst.de>
Date: Mon, 26 Oct 2015 19:02:16 +0100
From: Torsten Duwe <duwe@....de>
To: Steven Rostedt <rostedt@...dmis.org>,
Michael Ellerman <mpe@...erman.id.au>
Cc: Jiri Kosina <jkosina@...e.cz>, linuxppc-dev@...ts.ozlabs.org,
linux-kernel@...r.kernel.org, live-patching@...r.kernel.org
Subject: [PATCH v3 7/8] Implement kernel live patching for ppc64le (ABIv2)
* create the appropriate files+functions
arch/powerpc/include/asm/livepatch.h
klp_check_compiler_support,
klp_arch_set_pc
arch/powerpc/kernel/livepatch.c with a stub for
klp_write_module_reloc
This is architecture-independent work in progress.
* introduce a fixup in arch/powerpc/kernel/entry_64.S
for local calls that are becoming global due to live patching.
And of course do the main KLP thing: return to a maybe different
address, possibly altered by the live patching ftrace op.
Signed-off-by: Torsten Duwe <duwe@...e.de>
---
arch/powerpc/include/asm/livepatch.h | 27 ++++++++++++++++++++
arch/powerpc/kernel/entry_64.S | 48 +++++++++++++++++++++++++++++++++---
arch/powerpc/kernel/livepatch.c | 20 +++++++++++++++
3 files changed, 91 insertions(+), 4 deletions(-)
create mode 100644 arch/powerpc/include/asm/livepatch.h
create mode 100644 arch/powerpc/kernel/livepatch.c
diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
new file mode 100644
index 0000000..334eb55
--- /dev/null
+++ b/arch/powerpc/include/asm/livepatch.h
@@ -0,0 +1,27 @@
+#ifndef _ASM_POWERPC64_LIVEPATCH_H
+#define _ASM_POWERPC64_LIVEPATCH_H
+
+#include <linux/module.h>
+#include <linux/ftrace.h>
+
+#ifdef CONFIG_LIVEPATCH
+static inline int klp_check_compiler_support(void)
+{
+#if !defined(_CALL_ELF) || _CALL_ELF != 2
+ return 1;
+#endif
+ return 0;
+}
+
+extern int klp_write_module_reloc(struct module *mod, unsigned long type,
+ unsigned long loc, unsigned long value);
+
+static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+{
+ regs->nip = ip;
+}
+#else
+#error Live patching support is disabled; check CONFIG_LIVEPATCH
+#endif
+
+#endif /* _ASM_POWERPC64_LIVEPATCH_H */
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index b0dfbfe..2681601 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -1264,6 +1264,9 @@ _GLOBAL(ftrace_caller)
mflr r3
std r3, _NIP(r1)
std r3, 16(r1)
+#ifdef CONFIG_LIVEPATCH
+ mr r14,r3 // remember "old" NIP
+#endif
subi r3, r3, MCOUNT_INSN_SIZE
mfmsr r4
std r4, _MSR(r1)
@@ -1280,7 +1283,10 @@ ftrace_call:
nop
ld r3, _NIP(r1)
- mtlr r3
+ mtctr r3 // prepare to jump there
+#ifdef CONFIG_LIVEPATCH
+ cmpd r14,r3 // has NIP been altered?
+#endif
REST_8GPRS(0,r1)
REST_8GPRS(8,r1)
@@ -1293,6 +1299,24 @@ ftrace_call:
mtlr r12
mr r2,r0 // restore callee's TOC
+#ifdef CONFIG_LIVEPATCH
+ beq+ 4f // likely(old_NIP == new_NIP)
+
+ // For a local call, restore this TOC after calling the patch function.
+ // For a global call, it does not matter what we restore here,
+ // since the global caller does its own restore right afterwards,
+ // anyway.
+ // Just insert a KLP_return_helper frame in any case,
+ // so a patch function can always count on the changed stack offsets.
+ stdu r1,-32(r1) // open new mini stack frame
+ std r0,24(r1) // save TOC now, unconditionally.
+ LOAD_REG_IMMEDIATE(r12,KLP_return_helper)
+ std r12,LRSAVE(r1)
+ mtlr r12
+ bctr
+4:
+#endif
+
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
stdu r1, -112(r1)
.globl ftrace_graph_call
@@ -1302,15 +1326,31 @@ _GLOBAL(ftrace_graph_stub)
addi r1, r1, 112
#endif
- mflr r0 // move this LR to CTR
- mtctr r0
-
ld r0,LRSAVE(r1) // restore callee's lr at _mcount site
mtlr r0
bctr // jump after _mcount site
#endif /* CC_USING_MPROFILE_KERNEL */
_GLOBAL(ftrace_stub)
blr
+
+#ifdef CONFIG_LIVEPATCH
+/* Helper function for local calls that are becoming global
+ due to live patching.
+ We can't simply patch the NOP after the original call,
+ because, depending on the consistency model, some kernel
+ threads may still have called the original, local function
+ *without* saving their TOC in the respective stack frame slot,
+ so the decision is made per-thread during function return by
+ maybe inserting a KLP_return_helper frame or not.
+*/
+KLP_return_helper:
+ ld r2,24(r1) // restore TOC (saved by ftrace_caller)
+ addi r1, r1, 32 // destroy mini stack frame
+ ld r0,LRSAVE(r1) // get the real return address
+ mtlr r0
+ blr
+#endif
+
#else
_GLOBAL_TOC(_mcount)
/* Taken from output of objdump from lib64/glibc */
diff --git a/arch/powerpc/kernel/livepatch.c b/arch/powerpc/kernel/livepatch.c
new file mode 100644
index 0000000..9dace38
--- /dev/null
+++ b/arch/powerpc/kernel/livepatch.c
@@ -0,0 +1,20 @@
+#include <linux/module.h>
+#include <asm/livepatch.h>
+
+/**
+ * klp_write_module_reloc() - write a relocation in a module
+ * @mod: module in which the section to be modified is found
+ * @type: ELF relocation type (see asm/elf.h)
+ * @loc: address that the relocation should be written to
+ * @value: relocation value (sym address + addend)
+ *
+ * This function writes a relocation to the specified location for
+ * a particular module.
+ */
+int klp_write_module_reloc(struct module *mod, unsigned long type,
+ unsigned long loc, unsigned long value)
+{
+ /* This requires infrastructure changes; we need the loadinfos. */
+ pr_err("lpc_write_module_reloc not yet supported\n");
+ return -ENOSYS;
+}
--
1.8.5.6
--
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