Messages in this thread Patch in this message | | | Date | Fri, 14 Jan 2022 12:24:52 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86/entry_32: Fix segment exceptions |
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On Thu, Jan 13, 2022 at 08:55:37PM +0100, Peter Zijlstra wrote: > On IRC Andrew also noted that these EX_REG_* things should be __i386__ > only. Previosly when they lived as open-coded EX_DATA_REG() usage in > entry_32.S that was implied, but now ...
I guess that then below.
amluto, I'd love it if we (and by that I mean you :-)) could document the rules for GS on 32-bit so that it is clear what's going on there...
entry_32.S is only hinting at what's going on, we have comments here and there but not all concentrated into a single location.
Thx.
--- From: Borislav Petkov <bp@suse.de> Date: Fri, 14 Jan 2022 12:15:21 +0100 Subject: [PATCH] x86/entry_32: Remove GS from the pt_regs offsets and fixup regs
GS is special on 32-bit and segment exceptions fixup through it won't work. Leave breadcrumbs for others not to walk into the same nasty.
Fixes: 9cdbeec40968 ("x86/entry_32: Fix segment exceptions") Signed-off-by: Borislav Petkov <bp@suse.de> --- arch/x86/include/asm/extable_fixup_types.h | 5 +++-- arch/x86/lib/insn-eval.c | 5 ++++- 2 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/arch/x86/include/asm/extable_fixup_types.h b/arch/x86/include/asm/extable_fixup_types.h index 503622627400..0aa5f4d3234f 100644 --- a/arch/x86/include/asm/extable_fixup_types.h +++ b/arch/x86/include/asm/extable_fixup_types.h @@ -20,11 +20,12 @@ #define EX_DATA_FLAG(flag) ((flag) << EX_DATA_FLAG_SHIFT) #define EX_DATA_IMM(imm) ((imm) << EX_DATA_IMM_SHIFT) -/* segment regs */ +#ifdef CONFIG_X86_32 +/* segment regs, valid only for 32-bit code, see pt_regoff */ #define EX_REG_DS EX_DATA_REG(8) #define EX_REG_ES EX_DATA_REG(9) #define EX_REG_FS EX_DATA_REG(10) -#define EX_REG_GS EX_DATA_REG(11) +#endif /* flags */ #define EX_FLAG_CLEAR_AX EX_DATA_FLAG(1) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index b781d324211b..34001eee7482 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -432,7 +432,10 @@ static const int pt_regoff[] = { offsetof(struct pt_regs, ds), offsetof(struct pt_regs, es), offsetof(struct pt_regs, fs), - offsetof(struct pt_regs, gs), + /* + * Can't use that one - it is special - see entry_32.S + * offsetof(struct pt_regs, gs), + */ #endif }; -- 2.29.2
-- Regards/Gruss, Boris.
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