Re: [RFC][PATCH] objtool: STAC/CLAC validation
flat view
From: Peter Zijlstra <peterz@infradead.org>
Date: 2019-02-25 11:54:05
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lkml
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
On Mon, Feb 25, 2019 at 11:51:44AM +0100, Peter Zijlstra wrote:
On Fri, Feb 22, 2019 at 03:55:25PM -0800, Andy Lutomirski wrote:quoted
I'm wondering if we can just change the code that does getreg() and load_gs_index() so it doesn't do it with AC set. Also, what about paravirt kernels? They'll call into PV code for load_gs_index() with AC set.Paravirt can go bugger off. There's no sane way to fix that.
I don't fully understand that code at all; I also have no clue why GS has paravirt bits on but the other segments do not.
*sigh* SWAPGS
*thought*... we could delay the actual set_user_seg() thing until after the get_user_catch(), would that work?
How horrible / broken is this? ---
diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 321fe5f5d0e9..67c866943102 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c@@ -60,17 +60,21 @@ regs->seg = GET_SEG(seg) | 3; \ } while (0) -#define RELOAD_SEG(seg) { \ - unsigned int pre = GET_SEG(seg); \ - unsigned int cur = get_user_seg(seg); \ - pre |= 3; \ - if (pre != cur) \ - set_user_seg(seg, pre); \ +#define LOAD_SEG(seg) { \ + pre_##seg = 3 | GET_SEG(seg); \ + cur_##seg = get_user_seg(seg); \ +} + +#define RELOAD_SEG(seg) { \ + if (pre_##seg != cur_##seg) \ + set_user_seg(seg, pre_##seg); \ } static int ia32_restore_sigcontext(struct pt_regs *regs, struct sigcontext_32 __user *sc) { + u16 pre_gs, pre_fs, pre_ds, pre_es; + u16 cur_gs, cur_fs, cur_ds, cur_es; unsigned int tmpflags, err = 0; void __user *buf; u32 tmp;
@@ -85,10 +89,10 @@ static int ia32_restore_sigcontext(struct pt_regs *regs, * the handler, but does not clobber them at least in the * normal case. */ - RELOAD_SEG(gs); - RELOAD_SEG(fs); - RELOAD_SEG(ds); - RELOAD_SEG(es); + LOAD_SEG(gs); + LOAD_SEG(fs); + LOAD_SEG(ds); + LOAD_SEG(es); COPY(di); COPY(si); COPY(bp); COPY(sp); COPY(bx); COPY(dx); COPY(cx); COPY(ip); COPY(ax);
@@ -106,6 +110,11 @@ static int ia32_restore_sigcontext(struct pt_regs *regs, buf = compat_ptr(tmp); } get_user_catch(err); + RELOAD_SEG(gs); + RELOAD_SEG(fs); + RELOAD_SEG(ds); + RELOAD_SEG(es); + err |= fpu__restore_sig(buf, 1); force_iret();
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