linux-kernel - [PATCH v3] MIPS: Fix MAX_REG

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Message-ID: <20250427113423.67040-2-thorsten.blum@linux.dev>
Date: Sun, 27 Apr 2025 13:34:24 +0200
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Oleg Nesterov <oleg@...hat.com>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: "Maciej W. Rozycki" <macro@...am.me.uk>,
	Thorsten Blum <thorsten.blum@...ux.dev>,
	linux-mips@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v3] MIPS: Fix MAX_REG_OFFSET

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@...ux.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