[PATCH v2 1/2] powerpc/64s: system call scv tabort fix for corrupt irq soft-mask state

[Christophe Leroy]

Le 01/09/2021 à 18:54, Nicholas Piggin a écrit :
> If a system call is made with a transaction active, the kernel
> immediately aborts it and returns. scv system calls disable irqs even
> earlier in their interrupt handler, and tabort_syscall does not fix this
> up.
> 
> This can result in irq soft-mask state being messed up on the next
> kernel entry, and crashing at BUG_ON(arch_irq_disabled_regs(regs)) in
> the kernel exit handlers, or possibly worse.
> 
> Fix this by having tabort_syscall setting irq soft-mask back to enabled
> (which requires MSR[EE] be disabled first).
> 
> Reported-by: Eirik Fuller <efuller at redhat.com>
> Fixes: 7fa95f9adaee7 ("powerpc/64s: system call support for scv/rfscv instructions")
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> 
> Tested the wrong kernel before sending v1 and missed a bug, sorry.
> 
>   arch/powerpc/kernel/interrupt_64.S | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
> index d4212d2ff0b5..9c31d65b4851 100644
> --- a/arch/powerpc/kernel/interrupt_64.S
> +++ b/arch/powerpc/kernel/interrupt_64.S
> @@ -428,16 +428,22 @@ RESTART_TABLE(.Lsyscall_rst_start, .Lsyscall_rst_end, syscall_restart)
>   #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
>   tabort_syscall:
>   _ASM_NOKPROBE_SYMBOL(tabort_syscall)
> -	/* Firstly we need to enable TM in the kernel */
> +	/* We need to enable TM in the kernel, and disable EE (for scv) */
>   	mfmsr	r10
>   	li	r9, 1
>   	rldimi	r10, r9, MSR_TM_LG, 63-MSR_TM_LG
> +	LOAD_REG_IMMEDIATE(r9, MSR_EE)
> +	andc	r10, r10, r9

Why not use 'rlwinm' to mask out MSR_EE ?

Something like

	rlwinm	r10, r10, 0, ~MSR_EE

>   	mtmsrd	r10, 0
>   
>   	/* tabort, this dooms the transaction, nothing else */
>   	li	r9, (TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT)
>   	TABORT(R9)
>   
> +	/* scv has disabled irqs so must re-enable. sc just remains enabled */
> +	li	r9,IRQS_ENABLED
> +	stb	r9,PACAIRQSOFTMASK(r13)
> +
>   	/*
>   	 * Return directly to userspace. We have corrupted user register state,
>   	 * but userspace will never see that register state. Execution will
>