This is heavily copied from PPC64. Not much to say about it.
Livepatch sample modules all work.
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/powerpc/Kconfig | 2 +-
arch/powerpc/include/asm/livepatch.h | 4 +-
arch/powerpc/kernel/trace/ftrace_32.S | 69 +++++++++++++++++++++++++++
3 files changed, 72 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index f66eb1984b00..eceee3b814b9 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -230,7 +230,7 @@ config PPC
select HAVE_KPROBES_ON_FTRACE
select HAVE_KRETPROBES
select HAVE_LD_DEAD_CODE_DATA_ELIMINATION
- select HAVE_LIVEPATCH if HAVE_DYNAMIC_FTRACE_WITH_REGS && PPC64
+ select HAVE_LIVEPATCH if HAVE_DYNAMIC_FTRACE_WITH_REGS
select HAVE_MOD_ARCH_SPECIFIC
select HAVE_NMI if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
select HAVE_OPTPROBES
diff --git a/arch/powerpc/include/asm/livepatch.h b/arch/powerpc/include/asm/livepatch.h
index 4fe018cc207b..daf24d837241 100644
--- a/arch/powerpc/include/asm/livepatch.h
+++ b/arch/powerpc/include/asm/livepatch.h
@@ -23,8 +23,8 @@ static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
{
/*
- * Live patch works only with -mprofile-kernel on PPC. In this case,
- * the ftrace location is always within the first 16 bytes.
+ * Live patch works on PPC32 and only with -mprofile-kernel on PPC64. In
+ * both cases, the ftrace location is always within the first 16 bytes.
*/
return ftrace_location_range(faddr, faddr + 16);
}
diff --git a/arch/powerpc/kernel/trace/ftrace_32.S b/arch/powerpc/kernel/trace/ftrace_32.S
index 0a02c0cb12d9..2545d6bb9f02 100644
--- a/arch/powerpc/kernel/trace/ftrace_32.S
+++ b/arch/powerpc/kernel/trace/ftrace_32.S
@@ -10,6 +10,7 @@
#include <asm/ftrace.h>
#include <asm/export.h>
#include <asm/ptrace.h>
+#include <asm/bug.h>
_GLOBAL(mcount)
_GLOBAL(_mcount)
@@ -83,6 +84,9 @@ _GLOBAL(ftrace_regs_caller)
lis r3,function_trace_op@ha
lwz r5,function_trace_op@l(r3)
+#ifdef CONFIG_LIVEPATCH
+ mr r14,r7 /* remember old NIP */
+#endif
/* Calculate ip from nip-4 into r3 for call below */
subi r3, r7, MCOUNT_INSN_SIZE
@@ -107,6 +111,9 @@ ftrace_regs_call:
/* Load ctr with the possibly modified NIP */
lwz r3, _NIP(r1)
mtctr r3
+#ifdef CONFIG_LIVEPATCH
+ cmpw r14, r3 /* has NIP been altered? */
+#endif
/* Restore gprs */
lmw r2, GPR2(r1)
@@ -118,8 +125,70 @@ ftrace_regs_call:
/* Pop our stack frame */
addi r1, r1, INT_FRAME_SIZE
+#ifdef CONFIG_LIVEPATCH
+ /* Based on the cmpw above, if the NIP was altered handle livepatch */
+ bne- livepatch_handler
+#endif
b ftrace_caller_common
+#ifdef CONFIG_LIVEPATCH
+ /*
+ * This function runs in the mcount context, between two functions. As
+ * such it can only clobber registers which are volatile and used in
+ * function linkage.
+ *
+ * We get here when a function A, calls another function B, but B has
+ * been live patched with a new function C.
+ *
+ * On entry:
+ * - we have no stack frame and can not allocate one
+ * - LR points back to the original caller (in A)
+ * - CTR holds the new NIP in C
+ * - r0, r11 & r12 are free
+ */
+livepatch_handler:
+ /* Allocate 2 x 8 bytes */
+ lwz r11, TI_livepatch_sp+THREAD(r2)
+ addi r11, r11, 16
+ stw r11, TI_livepatch_sp+THREAD(r2)
+
+ /* Save real LR on livepatch stack */
+ mflr r12
+ stw r12, -16(r11)
+
+ /* Store stack end marker */
+ lis r12, STACK_END_MAGIC@h
+ ori r12, r12, STACK_END_MAGIC@l
+ stw r12, -4(r11)
+
+ /* Branch to ctr */
+ bctrl
+
+ /*
+ * Now we are returning from the patched function to the original
+ * caller A. We are free to use r11 and r12.
+ */
+
+ lwz r11, TI_livepatch_sp+THREAD(r2)
+
+ /* Check stack marker hasn't been trashed */
+ lwz r12, -4(r11)
+ subis r12, r12, STACK_END_MAGIC@h
+1: twnei r12, STACK_END_MAGIC@l
+ EMIT_BUG_ENTRY 1b, __FILE__, __LINE__ - 1, 0
+
+ /* Restore LR from livepatch stack */
+ lwz r12, -16(r11)
+ mtlr r12
+
+ /* Pop livepatch stack frame */
+ subi r11, r11, 16
+ stw r11, TI_livepatch_sp+THREAD(r2)
+
+ /* Return to original caller of live patched function */
+ blr
+#endif /* CONFIG_LIVEPATCH */
+
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
_GLOBAL(ftrace_graph_caller)
stwu r1,-48(r1)
--
2.31.1
