Commit 1400eb6 (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: James Hogan <james.hogan@xxxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: Gregory Fong <gregory.0xf0@xxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxx Cc: stable@xxxxxxxxxxxxxxx #3.11 --- Ralf: This is a regression in v3.11, so please consider for v3.12. arch/mips/kernel/octeon_switch.S | 2 +- arch/mips/kernel/r2300_switch.S | 2 +- arch/mips/kernel/r4k_switch.S | 2 +- 3 files changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/mips/kernel/octeon_switch.S b/arch/mips/kernel/octeon_switch.S index 4204d76..029e002 100644 --- a/arch/mips/kernel/octeon_switch.S +++ b/arch/mips/kernel/octeon_switch.S @@ -73,7 +73,7 @@ 3: #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_S t9, 0(t8) #endif diff --git a/arch/mips/kernel/r2300_switch.S b/arch/mips/kernel/r2300_switch.S index 38af83f..20b7b04 100644 --- a/arch/mips/kernel/r2300_switch.S +++ b/arch/mips/kernel/r2300_switch.S @@ -67,7 +67,7 @@ LEAF(resume) 1: #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_S t9, 0(t8) #endif diff --git a/arch/mips/kernel/r4k_switch.S b/arch/mips/kernel/r4k_switch.S index 921238a..078de5e 100644 --- a/arch/mips/kernel/r4k_switch.S +++ b/arch/mips/kernel/r4k_switch.S @@ -69,7 +69,7 @@ 1: #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_S t9, 0(t8) #endif -- 1.8.1.2
