On Wed, Jan 10, 2024 at 10:56 PM Kees Cook [off-list ref] wrote:

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@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Walleij <redacted>
Cc: Vladimir Murzin <redacted>
Cc: Zhen Lei <redacted>
Cc: Keith Packard <redacted>
Cc: Haibo Li <redacted>
Cc: linux-arm-kernel@lists.infradead.org
Signed-off-by: Kees Cook <redacted>

Makes sense.
Reviewed-by: Linus Walleij <redacted>

Yours,
Linus Walleij

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