[PATCH] powerpc/32: Fix hardlockup on vmap stack overflow

[PATCH] powerpc/32: Fix hardlockup on vmap stack overflow

[Christophe Leroy]

Since the commit c118c7303ad5 ("powerpc/32: Fix vmap stack - Do not
activate MMU before reading task struct") a vmap stack overflow
results in a hard lockup. This is because emergency_ctx is still
addressed with its virtual address allthough data MMU is not active
anymore at that time.

Fix it by using a physical address instead.

Fixes: c118c7303ad5 ("powerpc/32: Fix vmap stack - Do not activate MMU before reading task struct")
Cc: stable@vger.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 arch/powerpc/kernel/head_32.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index 6b1ec9e3541b..349c4a820231 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -202,11 +202,11 @@ _ASM_NOKPROBE_SYMBOL(\name\()_virt)
 	mfspr	r1, SPRN_SPRG_THREAD
 	lwz	r1, TASK_CPU - THREAD(r1)
 	slwi	r1, r1, 3
-	addis	r1, r1, emergency_ctx@ha
+	addis	r1, r1, emergency_ctx-PAGE_OFFSET@ha
 #else
-	lis	r1, emergency_ctx@ha
+	lis	r1, emergency_ctx-PAGE_OFFSET@ha
 #endif
-	lwz	r1, emergency_ctx@l(r1)
+	lwz	r1, emergency_ctx-PAGE_OFFSET@l(r1)
 	addi	r1, r1, THREAD_SIZE - INT_FRAME_SIZE
 	EXCEPTION_PROLOG_2 0 vmap_stack_overflow
 	prepare_transfer_to_handler
-- 
2.33.1

Re: [PATCH] powerpc/32: Fix hardlockup on vmap stack overflow

[Michael Ellerman]

On Thu, 18 Nov 2021 10:39:53 +0100, Christophe Leroy wrote:
> Since the commit c118c7303ad5 ("powerpc/32: Fix vmap stack - Do not
> activate MMU before reading task struct") a vmap stack overflow
> results in a hard lockup. This is because emergency_ctx is still
> addressed with its virtual address allthough data MMU is not active
> anymore at that time.
> 
> Fix it by using a physical address instead.
> 
> [...]

Applied to powerpc/fixes.

[1/1] powerpc/32: Fix hardlockup on vmap stack overflow
      https://git.kernel.org/powerpc/c/5bb60ea611db1e04814426ed4bd1c95d1487678e

cheers