Re: [PATCH] powerpc/ptrace: Add offsetof check for exit_flags in pt_regs_check()
From: Amit Machhiwal <hidden>
Date: 2026-07-03 08:56:05
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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: stable@vger.kernel.org
quoted hunk ↗ jump to hunk
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <redacted> --- 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 <redacted> Thanks, Amit
BUILD_BUG_ON(sizeof(struct user_pt_regs) > sizeof(struct pt_regs)); -- 2.55.0