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x86/asm/32: Make pt_regs's segment registers be 16 bits

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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@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2017-07-28 06:00:30 -07:00 committed by Ingo Molnar
parent 21ec3bf6ae
commit 385eca8f27
1 changed files with 26 additions and 6 deletions
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32
arch/x86/include/asm/ptrace.h
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@ -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__ */