MIPS: Fix MAX_REG_OFFSET

BugLink: https://bugs.launchpad.net/bugs/2115252

[ Upstream commit c44572e ]

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: 40e084a ("MIPS: Add uprobes support.")
Suggested-by: Maciej W. Rozycki <[email protected]>
Signed-off-by: Thorsten Blum <[email protected]>
Signed-off-by: Thomas Bogendoerfer <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
Signed-off-by: Manuel Diewald <[email protected]>
Signed-off-by: Stefan Bader <[email protected]>

Author: toblux

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