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ARM: 8266/1: Remove early stack deallocation from restore_user_regs

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Currently restore_user_regs deallocates the SVC stack early in
its execution and relies on no exception being taken between
the deallocation and the registers being restored. The introduction
of a default FIQ handler that also uses the SVC stack breaks this
assumption and can result in corrupted register state.

This patch works around the problem by removing the early
stack deallocation and using r2 as a temporary instead. I have
not found a way to do this without introducing an extra mov
instruction to the macro.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Daniel Thompson 2015-01-09 18:30:13 +01:00 committed by Russell King
parent 1e3479225a
commit a18f36453e
1 changed files with 7 additions and 6 deletions
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13
arch/arm/kernel/entry-header.S
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@ -253,21 +253,22 @@
.endm
.macro restore_user_regs, fast = 0, offset = 0
ldr r1, [sp, #\offset + S_PSR] @ get calling cpsr
ldr lr, [sp, #\offset + S_PC]! @ get pc
mov r2, sp
ldr r1, [r2, #\offset + S_PSR] @ get calling cpsr
ldr lr, [r2, #\offset + S_PC]! @ get pc
msr spsr_cxsf, r1 @ save in spsr_svc
#if defined(CONFIG_CPU_V6) || defined(CONFIG_CPU_32v6K)
@ We must avoid clrex due to Cortex-A15 erratum #830321
strex r1, r2, [sp] @ clear the exclusive monitor
strex r1, r2, [r2] @ clear the exclusive monitor
#endif
.if \fast
ldmdb sp, {r1 - lr}^ @ get calling r1 - lr
ldmdb r2, {r1 - lr}^ @ get calling r1 - lr
.else
ldmdb sp, {r0 - lr}^ @ get calling r0 - lr
ldmdb r2, {r0 - lr}^ @ get calling r0 - lr
.endif
mov r0, r0 @ ARMv5T and earlier require a nop
@ after ldm {}^
add sp, sp, #S_FRAME_SIZE - S_PC
add sp, sp, #\offset + S_FRAME_SIZE
movs pc, lr @ return & move spsr_svc into cpsr
.endm