Re: [PATCH RFC] arm64/scs: Fix potential sign extension issue of advance_loc4

[Catalin Marinas <catalin.marinas@arm.com>]

On Mon, Apr 13, 2026 at 05:54:59PM +0800, Wentao Guan wrote:
> The expression (*opcode++ << 24) and exp * code_alignment_factor
> may overflow signed int and becomes negative.
> 
> Fix this by casting each byte to u64 before shifting. Also fix
> the misaligned break statement while we are here.
> 
> Example of the result can be seen here:
> Link: https://godbolt.org/z/zhY8d3595
> 
> It maybe not a real problem, but could be a issue in future.
> 
> Fixes: d499e9627d70 ("arm64/scs: Fix handling of advance_loc4")
> Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
> ---
>  arch/arm64/kernel/pi/patch-scs.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/pi/patch-scs.c b/arch/arm64/kernel/pi/patch-scs.c
> index dac568e4a54f2..3944ad899021c 100644
> --- a/arch/arm64/kernel/pi/patch-scs.c
> +++ b/arch/arm64/kernel/pi/patch-scs.c
> @@ -196,9 +196,9 @@ static int scs_handle_fde_frame(const struct eh_frame *frame,
>  			loc += *opcode++ * code_alignment_factor;
>  			loc += (*opcode++ << 8) * code_alignment_factor;
>  			loc += (*opcode++ << 16) * code_alignment_factor;
> -			loc += (*opcode++ << 24) * code_alignment_factor;
> +			loc += ((u64)*opcode++ << 24) * code_alignment_factor;
>  			size -= 4;
> -		break;
> +			break;

The fix makes sense. I'll queue it at -rc1.

Thanks.

-- 
Catalin