Re: [PATCH v3] MIPS: Fix MAX_REG_OFFSET

[Thomas Bogendoerfer <tsbogend@alpha.franken.de>]

On Sun, Apr 27, 2025 at 01:34:24PM +0200, Thorsten Blum wrote:
> Fix MAX_REG_OFFSET to point to the last register in 'pt_regs' and not to
> the marker itself, which could allow regs_get_register() to return an
> invalid offset.
> 
> Fixes: 40e084a506eb ("MIPS: Add uprobes support.")
> Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
> ---
> Compile-tested only.
> 
> Changes in v2:
> - Fix MAX_REG_OFFSET as suggested by Maciej (thanks!)
> - Link to v1: https://lore.kernel.org/lkml/20250411090032.7844-1-thorsten.blum@linux.dev/
> 
> Changes in v3:
> - Keep the marker and avoid using #ifdef by adjusting MAX_REG_OFFSET as
>   suggested by Thomas and Maciej
> - Link to v2: https://lore.kernel.org/lkml/20250417174712.69292-2-thorsten.blum@linux.dev/
> ---
>  arch/mips/include/asm/ptrace.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/mips/include/asm/ptrace.h b/arch/mips/include/asm/ptrace.h
> index 85fa9962266a..ef72c46b5568 100644
> --- a/arch/mips/include/asm/ptrace.h
> +++ b/arch/mips/include/asm/ptrace.h
> @@ -65,7 +65,8 @@ static inline void instruction_pointer_set(struct pt_regs *regs,
>  
>  /* Query offset/name of register from its name/offset */
>  extern int regs_query_register_offset(const char *name);
> -#define MAX_REG_OFFSET (offsetof(struct pt_regs, __last))
> +#define MAX_REG_OFFSET \
> +	(offsetof(struct pt_regs, __last) - sizeof(unsigned long))
>  
>  /**
>   * regs_get_register() - get register value from its offset
> -- 
> 2.49.0

applied to mips-fixes.

Thomas.

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