[PATCH] x86/unwind/orc: Handle kretprobes_trampoline

[Kees Cook]

From: Marios Pomonis <pomonis@xxxxxxxxxx>

Fix a bug in the ORC unwinder when kretprobes has replaced a return
address with the address of `kretprobes_trampoline'. ORC mistakenly
assumes that the address in the stack is a return address and decrements
it by 1 in order to find the proper depth of the next frame.

This issue was discovered while testing the FG-KASLR series[0][1] and
running the live patching test[2] that was originally failing[3].

[0] https://lore.kernel.org/kernel-hardening/20200923173905.11219-1-kristen@xxxxxxxxxxxxxxx/
[1] https://github.com/KSPP/linux/issues/132
[2] https://github.com/lpechacek/qa_test_klp
[3] https://lore.kernel.org/lkml/alpine.LSU.2.21.2009251450260.13615@xxxxxxxxxxxxx/

Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
Signed-off-by: Marios Pomonis <pomonis@xxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Alexander Lobakin <alexandr.lobakin@xxxxxxxxx>
Cc: Kristen C Accardi <kristen.c.accardi@xxxxxxxxx>
Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 arch/x86/kernel/unwind_orc.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index a1202536fc57..8c5038b3b707 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -7,6 +7,7 @@
 #include <asm/unwind.h>
 #include <asm/orc_types.h>
 #include <asm/orc_lookup.h>
+#include <asm/kprobes.h>
 
 #define orc_warn(fmt, ...) \
 	printk_deferred_once(KERN_WARNING "WARNING: " fmt, ##__VA_ARGS__)
@@ -414,6 +415,15 @@ static bool get_reg(struct unwind_state *state, unsigned int reg_off,
 	return false;
 }
 
+static bool is_kretprobe_trampoline(unsigned long ip)
+{
+#ifdef	CONFIG_KRETPROBES
+	if (ip == (unsigned long)&kretprobe_trampoline)
+		return true;
+#endif
+	return false;
+}
+
 bool unwind_next_frame(struct unwind_state *state)
 {
 	unsigned long ip_p, sp, tmp, orig_ip = state->ip, prev_sp = state->sp;
@@ -540,7 +550,7 @@ bool unwind_next_frame(struct unwind_state *state)
 		state->sp = sp;
 		state->regs = NULL;
 		state->prev_regs = NULL;
-		state->signal = false;
+		state->signal = is_kretprobe_trampoline(state->ip);
 		break;
 
 	case UNWIND_HINT_TYPE_REGS:
-- 
2.30.2