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Date:   Thu,  2 Sep 2021 19:13:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Marios Pomonis <pomonis@...gle.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Kristen C Accardi <kristen.c.accardi@...el.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ivan Babrou <ivan@...udflare.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Julien Thierry <jthierry@...hat.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] x86/unwind/orc: Handle kretprobes_trampoline

From: Marios Pomonis <pomonis@...gle.com>

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@linux.intel.com/
[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@pobox.suse.cz/

Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
Signed-off-by: Marios Pomonis <pomonis@...gle.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Alexander Lobakin <alexandr.lobakin@...el.com>
Cc: Kristen C Accardi <kristen.c.accardi@...el.com>
Cc: Sami Tolvanen <samitolvanen@...gle.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 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

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