On 2026/07/03 01:19 PM, Mukesh Kumar Chaurasiya (IBM) wrote:
> pt_regs_check() verifies that fields shared between struct pt_regs and
> struct user_pt_regs sit at the same offset, to catch any accidental
> layout divergence between the kernel and uapi structures.
>
> Add the missing check for exit_flags, following the same pattern as the
> existing checks for result, dsisr, dar and the other shared fields.
>
> Fixes: d7a6797e0bc1 ("powerpc: add exit_flags field in pt_regs")
You may want to add below in order to get this patch backported:
Cc: [email protected]
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <[email protected]>
> ---
> arch/powerpc/kernel/ptrace/ptrace.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/kernel/ptrace/ptrace.c
> b/arch/powerpc/kernel/ptrace/ptrace.c
> index 316d4f5ead8e..fb3fec73f66a 100644
> --- a/arch/powerpc/kernel/ptrace/ptrace.c
> +++ b/arch/powerpc/kernel/ptrace/ptrace.c
> @@ -235,6 +235,8 @@ void __init pt_regs_check(void)
> offsetof(struct user_pt_regs, dsisr));
> BUILD_BUG_ON(offsetof(struct pt_regs, result) !=
> offsetof(struct user_pt_regs, result));
> + BUILD_BUG_ON(offsetof(struct pt_regs, exit_flags) !=
> + offsetof(struct user_pt_regs, exit_flags));
At first, it appeared to be redundant as we already check
CHECK_REG(PT_EXIT_FLAGS, exit_flags);
which expands to:
#define CHECK_REG(_pt, _reg) \
BUILD_BUG_ON(_pt != (offsetof(struct user_pt_regs, _reg) / \
sizeof(unsigned long)));
But looking closely, it turns out to be non-redundant. CHECK_REG only
touches struct user_pt_regs — it validates the PT_EXIT_FLAGS constant
against the uapi layout. It says nothing about struct pt_regs.
struct pt_regs (asm/ptrace.h) embeds struct user_pt_regs in a union
alongside an anonymous struct that re-declares all the same fields with
kernel-internal aliases (dear/dar, esr/dsisr). exit_flags lives in that
anonymous struct. A field accidentally inserted there between result and
exit_flags would silently break the union aliasing without CHECK_REG
catching it. The new BUILD_BUG_ON closes that gap, consistent with how
result, dar and dsisr are already protected in the same block.
Looks good to me.
Reviewed-by: Amit Machhiwal <[email protected]>
Thanks,
Amit
>
> BUILD_BUG_ON(sizeof(struct user_pt_regs) > sizeof(struct pt_regs));
>
> --
> 2.55.0
>
>
