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authorNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>2017-06-01 16:18:17 +0530
committerMichael Ellerman <mpe@ellerman.id.au>2017-06-16 19:49:43 +1000
commitc05b8c4474c03026aaa7f8872e78369f69f1bb08 (patch)
tree0dec69ce1815755aec7d8cd7f4c1cdd33226b37f
parenta4979a7e71eb8da976cbe4a0a1fa50636e76b04f (diff)
downloadop-kernel-dev-c05b8c4474c03026aaa7f8872e78369f69f1bb08.zip
op-kernel-dev-c05b8c4474c03026aaa7f8872e78369f69f1bb08.tar.gz
powerpc/kprobes: Skip livepatch_handler() for jprobes
ftrace_caller() depends on a modified regs->nip to detect if a certain function has been livepatched. However, with KPROBES_ON_FTRACE, it is possible for regs->nip to have been modified by the kprobes pre_handler (jprobes, for instance). In this case, we do not want to invoke the livepatch_handler so as not to consume the livepatch stack. To distinguish between the two (kprobes and livepatch), we check if there is an active kprobe on the current function. If there is, then we know for sure that it must have modified the NIP as we don't support livepatching a kprobe'd function. In this case, we simply skip the livepatch_handler and branch to the new NIP. Otherwise, the livepatch_handler is invoked. Fixes: ead514d5fb30 ("powerpc/kprobes: Add support for KPROBES_ON_FTRACE") Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
-rw-r--r--arch/powerpc/include/asm/kprobes.h1
-rw-r--r--arch/powerpc/kernel/kprobes.c6
-rw-r--r--arch/powerpc/kernel/trace/ftrace_64_mprofile.S39
3 files changed, 41 insertions, 5 deletions
diff --git a/arch/powerpc/include/asm/kprobes.h b/arch/powerpc/include/asm/kprobes.h
index a83821f..8814a72 100644
--- a/arch/powerpc/include/asm/kprobes.h
+++ b/arch/powerpc/include/asm/kprobes.h
@@ -103,6 +103,7 @@ extern int kprobe_exceptions_notify(struct notifier_block *self,
extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
extern int kprobe_handler(struct pt_regs *regs);
extern int kprobe_post_handler(struct pt_regs *regs);
+extern int is_current_kprobe_addr(unsigned long addr);
#ifdef CONFIG_KPROBES_ON_FTRACE
extern int skip_singlestep(struct kprobe *p, struct pt_regs *regs,
struct kprobe_ctlblk *kcb);
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 5075a4d..01addfb 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -43,6 +43,12 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
struct kretprobe_blackpoint kretprobe_blacklist[] = {{NULL, NULL}};
+int is_current_kprobe_addr(unsigned long addr)
+{
+ struct kprobe *p = kprobe_running();
+ return (p && (unsigned long)p->addr == addr) ? 1 : 0;
+}
+
bool arch_within_kprobe_blacklist(unsigned long addr)
{
return (addr >= (unsigned long)__kprobes_text_start &&
diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
index fa09214..c98e90b 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
+++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
@@ -99,13 +99,39 @@ ftrace_call:
bl ftrace_stub
nop
- /* Load ctr with the possibly modified NIP */
- ld r3, _NIP(r1)
- mtctr r3
+ /* Load the possibly modified NIP */
+ ld r15, _NIP(r1)
+
#ifdef CONFIG_LIVEPATCH
- cmpd r14,r3 /* has NIP been altered? */
+ cmpd r14, r15 /* has NIP been altered? */
#endif
+#if defined(CONFIG_LIVEPATCH) && defined(CONFIG_KPROBES_ON_FTRACE)
+ /* NIP has not been altered, skip over further checks */
+ beq 1f
+
+ /* Check if there is an active kprobe on us */
+ subi r3, r14, 4
+ bl is_current_kprobe_addr
+ nop
+
+ /*
+ * If r3 == 1, then this is a kprobe/jprobe.
+ * else, this is livepatched function.
+ *
+ * The conditional branch for livepatch_handler below will use the
+ * result of this comparison. For kprobe/jprobe, we just need to branch to
+ * the new NIP, not call livepatch_handler. The branch below is bne, so we
+ * want CR0[EQ] to be true if this is a kprobe/jprobe. Which means we want
+ * CR0[EQ] = (r3 == 1).
+ */
+ cmpdi r3, 1
+1:
+#endif
+
+ /* Load CTR with the possibly modified NIP */
+ mtctr r15
+
/* Restore gprs */
REST_GPR(0,r1)
REST_10GPRS(2,r1)
@@ -123,7 +149,10 @@ ftrace_call:
addi r1, r1, SWITCH_FRAME_SIZE
#ifdef CONFIG_LIVEPATCH
- /* Based on the cmpd above, if the NIP was altered handle livepatch */
+ /*
+ * Based on the cmpd or cmpdi above, if the NIP was altered and we're
+ * not on a kprobe/jprobe, then handle livepatch.
+ */
bne- livepatch_handler
#endif
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