Commit d5c24398 authored Dec 21, 2020 by Christophe Leroy Committed by Michael Ellerman Dec 21, 2020

powerpc/32: Fix vmap stack - Properly set r1 before activating MMU on syscall too

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: da7bb43a ("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

parent 2eda7f11

arch/powerpc/kernel/head_32.h

+16 −9

Original line number	Diff line number	Diff line
		@@ -121,18 +121,28 @@
		#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
		@@ -140,9 +150,6 @@
		#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 */

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