[PATCH 5.10 607/717] powerpc/32: Fix vmap stack - Properly set r1 before activating MMU on syscall too

Greg Kroah-Hartman
2020-12-28T14:42:12Z

From: Christophe Leroy <christophe.leroy@csgroup.eu>

commit d5c243989fb0cb03c74d7340daca3b819f706ee7 upstream.

We need r1 to be properly set before activating MMU, otherwise any new
exception taken while saving registers into the stack in syscall
prologs will use the user stack, which is wrong and will even lockup
or crash when KUAP is selected.

Do that by switching the meaning of r11 and r1 until we have saved r1
to the stack: copy r1 into r11 and setup the new stack pointer in r1.
To avoid complicating and impacting all generic and specific prolog
code (and more), copy back r1 into r11 once r11 is save onto
the stack.

We could get rid of copying r1 back and forth at the cost of rewriting
everything to use r1 instead of r11 all the way when CONFIG_VMAP_STACK
is set, but the effort is probably not worth it for now.

Fixes: da7bb43ab9da ("powerpc/32: Fix vmap stack - Properly set r1 before activating MMU")
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a3d819d5c348cee9783a311d5d3f3ba9b48fd219.1608531452.git.christophe.leroy@csgroup.eu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/powerpc/kernel/head_32.h | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)

--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -131,18 +131,28 @@
#ifdef CONFIG_VMAP_STACK
mfspr r11, SPRN_SRR0
mtctr r11
-#endif
andi. r11, r9, MSR_PR
- lwz r11,TASK_STACK-THREAD(r12)
+ mr r11, r1
+ lwz r1,TASK_STACK-THREAD(r12)
beq- 99f
- addi r11, r11, THREAD_SIZE - INT_FRAME_SIZE
-#ifdef CONFIG_VMAP_STACK
+ addi r1, r1, THREAD_SIZE - INT_FRAME_SIZE
li r10, MSR_KERNEL & ~(MSR_IR | MSR_RI) /* can take DTLB miss */
mtmsr r10
isync
+ tovirt(r12, r12)
+ stw r11,GPR1(r1)
+ stw r11,0(r1)
+ mr r11, r1
+#else
+ andi. r11, r9, MSR_PR
+ lwz r11,TASK_STACK-THREAD(r12)
+ beq- 99f
+ addi r11, r11, THREAD_SIZE - INT_FRAME_SIZE
+ tophys(r11, r11)
+ stw r1,GPR1(r11)
+ stw r1,0(r11)
+ tovirt(r1, r11) /* set new kernel sp */
#endif
- tovirt_vmstack r12, r12
- tophys_novmstack r11, r11
mflr r10
stw r10, _LINK(r11)
#ifdef CONFIG_VMAP_STACK
@@ -150,9 +160,6 @@
#else
mfspr r10,SPRN_SRR0
#endif
- stw r1,GPR1(r11)
- stw r1,0(r11)
- tovirt_novmstack r1, r11 /* set new kernel sp */
stw r10,_NIP(r11)
mfcr r10
rlwinm r10,r10,0,4,2 /* Clear SO bit in CR */