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powerpc: Don't corrupt user registers on 32-bit

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Commit de79f7b9f6 ("powerpc: Put FP/VSX and VR state into structures")
modified load_up_fpu() and load_up_altivec() in such a way that they
now use r7 and r8.  Unfortunately, the callers of these functions on
32-bit machines then return to userspace via fast_exception_return,
which doesn't restore all of the volatile GPRs, but only r1, r3 -- r6
and r9 -- r12.  This was causing userspace segfaults and other
userspace misbehaviour on 32-bit machines.

This fixes the problem by changing the register usage of load_up_fpu()
and load_up_altivec() to avoid using r7 and r8 and instead use r6 and
r10.  This also adds comments to those functions saying which registers
may be used.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Tested-by: Scott Wood <scottwood@freescale.com> (on e500mc, so no altivec)
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Paul Mackerras 2013-10-23 09:40:02 +01:00 committed by Benjamin Herrenschmidt
parent 18461960cb
commit 955c1cab80
2 changed files with 17 additions and 12 deletions
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14
arch/powerpc/kernel/fpu.S
View file

@ -106,6 +106,8 @@ _GLOBAL(store_fp_state)
* and save its floating-point registers in its thread_struct.
* Load up this task's FP registers from its thread_struct,
* enable the FPU for the current task and return to the task.
* Note that on 32-bit this can only use registers that will be
* restored by fast_exception_return, i.e. r3 - r6, r10 and r11.
*/
_GLOBAL(load_up_fpu)
mfmsr r5
@ -131,10 +133,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_VSX)
beq 1f
toreal(r4)
addi r4,r4,THREAD /* want last_task_used_math->thread */
addi r8,r4,THREAD_FPSTATE
SAVE_32FPVSRS(0, R5, R8)
addi r10,r4,THREAD_FPSTATE
SAVE_32FPVSRS(0, R5, R10)
mffs fr0
stfd fr0,FPSTATE_FPSCR(r8)
stfd fr0,FPSTATE_FPSCR(r10)
PPC_LL r5,PT_REGS(r4)
toreal(r5)
PPC_LL r4,_MSR-STACK_FRAME_OVERHEAD(r5)
@ -157,10 +159,10 @@ END_FTR_SECTION_IFSET(CPU_FTR_VSX)
or r12,r12,r4
std r12,_MSR(r1)
#endif
addi r7,r5,THREAD_FPSTATE
lfd fr0,FPSTATE_FPSCR(r7)
addi r10,r5,THREAD_FPSTATE
lfd fr0,FPSTATE_FPSCR(r10)
MTFSF_L(fr0)
REST_32FPVSRS(0, R4, R7)
REST_32FPVSRS(0, R4, R10)
#ifndef CONFIG_SMP
subi r4,r5,THREAD
fromreal(r4)

15
arch/powerpc/kernel/vector.S
View file

@ -64,6 +64,9 @@ _GLOBAL(store_vr_state)
* Enables the VMX for use in the kernel on return.
* On SMP we know the VMX is free, since we give it up every
* switch (ie, no lazy save of the vector registers).
*
* Note that on 32-bit this can only use registers that will be
* restored by fast_exception_return, i.e. r3 - r6, r10 and r11.
*/
_GLOBAL(load_up_altivec)
mfmsr r5 /* grab the current MSR */
@ -89,11 +92,11 @@ _GLOBAL(load_up_altivec)
/* Save VMX state to last_task_used_altivec's THREAD struct */
toreal(r4)
addi r4,r4,THREAD
addi r7,r4,THREAD_VRSTATE
SAVE_32VRS(0,r5,r7)
addi r6,r4,THREAD_VRSTATE
SAVE_32VRS(0,r5,r6)
mfvscr vr0
li r10,VRSTATE_VSCR
stvx vr0,r10,r7
stvx vr0,r10,r6
/* Disable VMX for last_task_used_altivec */
PPC_LL r5,PT_REGS(r4)
toreal(r5)
@ -125,13 +128,13 @@ _GLOBAL(load_up_altivec)
oris r12,r12,MSR_VEC@h
std r12,_MSR(r1)
#endif
addi r7,r5,THREAD_VRSTATE
addi r6,r5,THREAD_VRSTATE
li r4,1
li r10,VRSTATE_VSCR
stw r4,THREAD_USED_VR(r5)
lvx vr0,r10,r7
lvx vr0,r10,r6
mtvscr vr0
REST_32VRS(0,r4,r7)
REST_32VRS(0,r4,r6)
#ifndef CONFIG_SMP
/* Update last_task_used_altivec to 'current' */
subi r4,r5,THREAD /* Back to 'current' */