Commit 8b3c569a authored by James Hogan's avatar James Hogan Committed by Ralf Baechle

MIPS: stack protector: Fix per-task canary switch

Commit 1400eb65 (MIPS: r4k,octeon,r2300: stack protector: change canary
per task) was merged in v3.11 and introduced assembly in the MIPS resume
functions to update the value of the current canary in
__stack_chk_guard. However it used PTR_L resulting in a load of the
canary value, instead of PTR_LA to construct its address. The value is
intended to be random but is then treated as an address in the
subsequent LONG_S (store).

This was observed to cause a fault and panic:

CPU 0 Unable to handle kernel paging request at virtual address 139fea20, epc == 8000cc0c, ra == 8034f2a4
Oops[#1]:
...
$24   : 139fea20 1e1f7cb6
...
Call Trace:
[<8000cc0c>] resume+0xac/0x118
[<8034f2a4>] __schedule+0x5f8/0x78c
[<8034f4e0>] schedule_preempt_disabled+0x20/0x2c
[<80348eec>] rest_init+0x74/0x84
[<804dc990>] start_kernel+0x43c/0x454
Code: 3c18804b  8f184030  8cb901f8 <af190000> 00c0e021  8cb002f0 8cb102f4  8cb202f8  8cb302fc

This can also be forced by modifying
arch/mips/include/asm/stackprotector.h so that the default
__stack_chk_guard value is more likely to be a bad (or unaligned)
pointer.

Fix it to use PTR_LA instead, to load the address of the canary value,
which the LONG_S can then use to write into it.

Reported-by: bobjones (via #mipslinux on IRC)
Signed-off-by: default avatarJames Hogan <james.hogan@imgtec.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Gregory Fong <gregory.0xf0@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/6026/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 162bdafa
...@@ -73,7 +73,7 @@ ...@@ -73,7 +73,7 @@
3: 3:
#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP) #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
PTR_L t8, __stack_chk_guard PTR_LA t8, __stack_chk_guard
LONG_L t9, TASK_STACK_CANARY(a1) LONG_L t9, TASK_STACK_CANARY(a1)
LONG_S t9, 0(t8) LONG_S t9, 0(t8)
#endif #endif
......
...@@ -67,7 +67,7 @@ LEAF(resume) ...@@ -67,7 +67,7 @@ LEAF(resume)
1: 1:
#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP) #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
PTR_L t8, __stack_chk_guard PTR_LA t8, __stack_chk_guard
LONG_L t9, TASK_STACK_CANARY(a1) LONG_L t9, TASK_STACK_CANARY(a1)
LONG_S t9, 0(t8) LONG_S t9, 0(t8)
#endif #endif
......
...@@ -69,7 +69,7 @@ ...@@ -69,7 +69,7 @@
1: 1:
#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP) #if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
PTR_L t8, __stack_chk_guard PTR_LA t8, __stack_chk_guard
LONG_L t9, TASK_STACK_CANARY(a1) LONG_L t9, TASK_STACK_CANARY(a1)
LONG_S t9, 0(t8) LONG_S t9, 0(t8)
#endif #endif
......
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