[PATCH] x86/asm/32: Fix regs_get_register() on segment registers

[Andy Lutomirski <luto@kernel.org>]

The segment register high words on x86_32 may contain garbage.
Teach regs_get_register() to read them as u16 instead of unsigned
long.

Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 arch/x86/include/asm/ptrace.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 2d3681083307..ca6cded447f5 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -196,6 +196,17 @@ static inline unsigned long regs_get_register(struct pt_regs *regs,
 	if (offset == offsetof(struct pt_regs, sp) &&
 	    regs->cs == __KERNEL_CS)
 		return kernel_stack_pointer(regs);
+
+	/* The selector fields are 16-bit. */
+	if (offset == offsetof(struct pt_regs, cs) ||
+	    offset == offsetof(struct pt_regs, ss) ||
+	    offset == offsetof(struct pt_regs, ds) ||
+	    offset == offsetof(struct pt_regs, es) ||
+	    offset == offsetof(struct pt_regs, fs) ||
+	    offset == offsetof(struct pt_regs, gs)) {
+		return *(u16 *)((unsigned long)regs + offset);
+
+	}
 #endif
 	return *(unsigned long *)((unsigned long)regs + offset);
 }
-- 
2.13.3