linux-hardening - [PATCH] ARM: unwind: Add missing "Call trace:" line

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Message-Id: <20240110215554.work.460-kees@kernel.org>
Date: Wed, 10 Jan 2024 13:56:01 -0800
From: Kees Cook <keescook@...omium.org>
To: Russell King <linux@...linux.org.uk>
Cc: Kees Cook <keescook@...omium.org>,
	Mark Brown <broonie@...nel.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	Vladimir Murzin <vladimir.murzin@....com>,
	Zhen Lei <thunder.leizhen@...wei.com>,
	Keith Packard <keithpac@...zon.com>,
	Haibo Li <haibo.li@...iatek.com>,
	linux-arm-kernel@...ts.infradead.org,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Alexandre Mergnat <amergnat@...libre.com>,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] ARM: unwind: Add missing "Call trace:" line

Every other architecture in Linux includes the line "Call trace:" before
backtraces. In some cases ARM would print "Backtrace:", but this was
only via 1 specific call path, and wasn't included in CPU Oops nor things
like KASAN, UBSAN, etc that called dump_stack(). Regularize this line
so CI systems and other things (like LKDTM) that depend on parsing
"Call trace:" out of dmesg will see it for ARM.

Before this patch:

	UBSAN: array-index-out-of-bounds in ../drivers/misc/lkdtm/bugs.c:376:16
	index 8 is out of range for type 'char [8]'
	CPU: 0 PID: 1402 Comm: cat Not tainted 6.7.0-rc2 #1
	Hardware name: Generic DT based system
	 dump_backtrace from show_stack+0x20/0x24
	 r7:00000042 r6:00000000 r5:60070013 r4:80cf5d7c
	 show_stack from dump_stack_lvl+0x88/0x98
	 dump_stack_lvl from dump_stack+0x18/0x1c
	 r7:00000042 r6:00000008 r5:00000008 r4:80fab118
	 dump_stack from ubsan_epilogue+0x10/0x3c
	 ubsan_epilogue from __ubsan_handle_out_of_bounds+0x80/0x84
	...

After this patch:

	UBSAN: array-index-out-of-bounds in ../drivers/misc/lkdtm/bugs.c:376:16
	index 8 is out of range for type 'char [8]'
	CPU: 0 PID: 1402 Comm: cat Not tainted 6.7.0-rc2 #1
	Hardware name: Generic DT based system
	Call trace:
	 dump_backtrace from show_stack+0x20/0x24
	 r7:00000042 r6:00000000 r5:60070013 r4:80cf5d7c
	 show_stack from dump_stack_lvl+0x88/0x98
	 dump_stack_lvl from dump_stack+0x18/0x1c
	 r7:00000042 r6:00000008 r5:00000008 r4:80fab118
	 dump_stack from ubsan_epilogue+0x10/0x3c
	 ubsan_epilogue from __ubsan_handle_out_of_bounds+0x80/0x84
	...

Reported-by: Mark Brown <broonie@...nel.org>
Cc: Russell King <linux@...linux.org.uk>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Linus Walleij <linus.walleij@...aro.org>
Cc: Vladimir Murzin <vladimir.murzin@....com>
Cc: Zhen Lei <thunder.leizhen@...wei.com>
Cc: Keith Packard <keithpac@...zon.com>
Cc: Haibo Li <haibo.li@...iatek.com>
Cc: linux-arm-kernel@...ts.infradead.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm/kernel/traps.c  | 2 +-
 arch/arm/kernel/unwind.c | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 3bad79db5d6e..72c82a4d63ac 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -220,7 +220,7 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 	unsigned int fp, mode;
 	int ok = 1;
 
-	printk("%sBacktrace: ", loglvl);
+	printk("%sCall trace: ", loglvl);
 
 	if (!tsk)
 		tsk = current;
diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index 9d2192156087..f60547dadc93 100644
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -524,6 +524,8 @@ void unwind_backtrace(struct pt_regs *regs, struct task_struct *tsk,
 {
 	struct stackframe frame;
 
+	printk("%sCall trace: ", loglvl);
+
 	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
 
 	if (!tsk)
-- 
2.34.1