[PATCH] powerpc/tm: do not use r13 for tabort_syscall

[Michael Neuling]

On Fri, 2016-07-22 at 17:27 +1000, Nicholas Piggin wrote:
> tabort_syscall runs with RI=1, so a nested recoverable machine
> check will load the paca into r13 and overwrite what we loaded
> it with, because exceptions returning to privileged mode do not
> restore r13.
> 
> This has survived testing with sc instruction inside transaction
> (bare sc, not glibc syscall because glibc can tabort before sc).
> Verified the transaction is failing failing with with
> TM_CAUSE_SYSCALL.
> 
> Signed-off-by: Nick Piggin <npiggin at gmail.com>
> Cc: Michael Neuling <mikey at neuling.org>

FWIW

Acked-by: Michael Neuling <mikey at neuling.org>

> Cc: Sam Bobroff <sam.bobroff at au1.ibm.com>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> 
> ---
> 
>  arch/powerpc/kernel/entry_64.S | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/entry_64.S
> b/arch/powerpc/kernel/entry_64.S
> index 73e461a..387dee3 100644
> --- a/arch/powerpc/kernel/entry_64.S
> +++ b/arch/powerpc/kernel/entry_64.S
> @@ -368,13 +368,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
>  tabort_syscall:
>  	/* Firstly we need to enable TM in the kernel */
>  	mfmsr	r10
> -	li	r13, 1
> -	rldimi	r10, r13, MSR_TM_LG, 63-MSR_TM_LG
> -	mtmsrd	r10, 0
> +	li	r9,1
> +	rldimi	r10,r9,MSR_TM_LG,63-MSR_TM_LG
> +	mtmsrd	r10,0
>  
>  	/* tabort, this dooms the transaction, nothing else */
> -	li	r13, (TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT)
> -	TABORT(R13)
> +	li	r9,(TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT)
> +	TABORT(R9)
>  
>  	/*
>  	 * Return directly to userspace. We have corrupted user register
> state,
> @@ -382,11 +382,11 @@ tabort_syscall:
>  	 * resume after the tbegin of the aborted transaction with the
>  	 * checkpointed register state.
>  	 */
> -	li	r13, MSR_RI
> -	andc	r10, r10, r13
> -	mtmsrd	r10, 1
> -	mtspr	SPRN_SRR0, r11
> -	mtspr	SPRN_SRR1, r12
> +	li	r9,MSR_RI
> +	andc	r10,r10,r9
> +	mtmsrd	r10,1
> +	mtspr	SPRN_SRR0,r11
> +	mtspr	SPRN_SRR1,r12
>  
>  	rfid
>  	b	.	/* prevent speculative execution */