[PATCH V2] powerpc: Restore KUAP registers on syscall restart exit

[PATCH V2] powerpc: Restore KUAP registers on syscall restart exit

[Mukesh Kumar Chaurasiya (IBM)]

During a syscall restart, block KUAP so that pending interrupts can be
replayed. The original KUAP state is not restored before returning to
userspace, causing subsequent userspace accesses to fault and eventually
trigger bad_access_pkey(), crashing the kernel.

The original KUAP register values are already saved in
arch_enter_from_user_mode(). Restore them on the syscall restart exit
path before returning to userspace.

Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
Reported-by: Sayali Patil <sayalip@linux.ibm.com>
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
---
V1 -> V2:
- Commit message rephrased
V1: https://lore.kernel.org/all/20260613123831.1510474-1-mkchauras@gmail.com

 arch/powerpc/kernel/interrupt.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 89a999be1352..f04978080837 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -166,6 +166,7 @@ notrace unsigned long syscall_exit_restart(unsigned long r3, struct pt_regs *reg
 		goto again;
 	}
 
+	kuap_user_restore(regs);
 	regs->exit_result |= regs->exit_flags;
 
 	return regs->exit_result;
-- 
2.54.0

Re: [PATCH V2] powerpc: Restore KUAP registers on syscall restart exit

[Sayali Patil]

On 15/06/26 21:56, Mukesh Kumar Chaurasiya (IBM) wrote:
> During a syscall restart, block KUAP so that pending interrupts can be
> replayed. The original KUAP state is not restored before returning to
> userspace, causing subsequent userspace accesses to fault and eventually
> trigger bad_access_pkey(), crashing the kernel.
> 
> The original KUAP register values are already saved in
> arch_enter_from_user_mode(). Restore them on the syscall restart exit
> path before returning to userspace.
> 
> Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
> Reported-by: Sayali Patil <sayalip@linux.ibm.com>
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
> ---
> V1 -> V2:
> - Commit message rephrased
> V1: https://lore.kernel.org/all/20260613123831.1510474-1-mkchauras@gmail.com
> 
>   arch/powerpc/kernel/interrupt.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index 89a999be1352..f04978080837 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -166,6 +166,7 @@ notrace unsigned long syscall_exit_restart(unsigned long r3, struct pt_regs *reg
>   		goto again;
>   	}
>   
> +	kuap_user_restore(regs);
>   	regs->exit_result |= regs->exit_flags;
>   
>   	return regs->exit_result;

This fixes the reported issue.

Tested-by: Sayali Patil <sayalip@linux.ibm.com>