Commit-ID: 385eca8f277c4c34f361a4c3a088fd876d29ae21
Gitweb: http://git.kernel.org/tip/385eca8f277c4c34f361a4c3a088fd876d29ae21
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Fri, 28 Jul 2017 06:00:30 -0700
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sun, 30 Jul 2017 12:04:40 +0200
x86/asm/32: Make pt_regs's segment registers be 16 bits
Many 32-bit x86 CPUs do 16-bit writes when storing segment registers to
memory. This can cause the high word of regs->[cdefgs]s to
occasionally contain garbage.
Rather than making the entry code more complicated to fix up the
garbage, just change pt_regs to reflect reality.
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Borislav Petkov <bpetkov@xxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/include/asm/ptrace.h | 32 ++++++++++++++++++++++++++------
1 file changed, 26 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 2b5d686..a29f828 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -9,6 +9,20 @@
#ifdef __i386__
struct pt_regs {
+ /*
+ * NB: 32-bit x86 CPUs are inconsistent as what happens in the
+ * following cases (where %seg represents a segment register):
+ *
+ * - pushl %seg: some do a 16-bit write and leave the high
+ * bits alone
+ * - movl %seg, [mem]: some do a 16-bit write despite the movl
+ * - IDT entry: some (e.g. 486) will leave the high bits of CS
+ * and (if applicable) SS undefined.
+ *
+ * Fortunately, x86-32 doesn't read the high bits on POP or IRET,
+ * so we can just treat all of the segment registers as 16-bit
+ * values.
+ */
unsigned long bx;
unsigned long cx;
unsigned long dx;
@@ -16,16 +30,22 @@ struct pt_regs {
unsigned long di;
unsigned long bp;
unsigned long ax;
- unsigned long ds;
- unsigned long es;
- unsigned long fs;
- unsigned long gs;
+ unsigned short ds;
+ unsigned short __dsh;
+ unsigned short es;
+ unsigned short __esh;
+ unsigned short fs;
+ unsigned short __fsh;
+ unsigned short gs;
+ unsigned short __gsh;
unsigned long orig_ax;
unsigned long ip;
- unsigned long cs;
+ unsigned short cs;
+ unsigned short __csh;
unsigned long flags;
unsigned long sp;
- unsigned long ss;
+ unsigned short ss;
+ unsigned short __ssh;
};
#else /* __i386__ */
--
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