linux/arch/mips/kernel/r4k_switch.S

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/*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file "COPYING" in the main directory of this archive
* for more details.
*
* Copyright (C) 1994, 1995, 1996, 1998, 1999, 2002, 2003 Ralf Baechle
* Copyright (C) 1996 David S. Miller (davem@davemloft.net)
* Copyright (C) 1994, 1995, 1996, by Andreas Busse
* Copyright (C) 1999 Silicon Graphics, Inc.
* Copyright (C) 2000 MIPS Technologies, Inc.
* written by Carsten Langgaard, carstenl@mips.com
*/
#include <asm/asm.h>
#include <asm/cachectl.h>
#include <asm/mipsregs.h>
#include <asm/asm-offsets.h>
#include <asm/regdef.h>
#include <asm/stackframe.h>
#include <asm/thread_info.h>
#include <asm/asmmacro.h>
/*
* task_struct *resume(task_struct *prev, task_struct *next,
* struct thread_info *next_ti)
*/
.align 5
LEAF(resume)
mfc0 t1, CP0_STATUS
LONG_S t1, THREAD_STATUS(a0)
cpu_save_nonscratch a0
LONG_S ra, THREAD_REG31(a0)
#if defined(CONFIG_CC_STACKPROTECTOR) && !defined(CONFIG_SMP)
MIPS: stack protector: Fix per-task canary switch 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@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: Ralf Baechle <ralf@linux-mips.org>
2013-10-07 19:14:26 +08:00
PTR_LA t8, __stack_chk_guard
LONG_L t9, TASK_STACK_CANARY(a1)
LONG_S t9, 0(t8)
#endif
/*
* The order of restoring the registers takes care of the race
* updating $28, $29 and kernelsp without disabling ints.
*/
move $28, a2
cpu_restore_nonscratch a1
PTR_ADDU t0, $28, _THREAD_SIZE - 32
set_saved_sp t0, t1, t2
mfc0 t1, CP0_STATUS /* Do we really need this? */
li a3, 0xff01
and t1, a3
LONG_L a2, THREAD_STATUS(a1)
nor a3, $0, a3
and a2, a3
or a2, t1
mtc0 a2, CP0_STATUS
move v0, a0
jr ra
END(resume)