On Fri, 2015-05-15 at 15:25 +0100, Ben Hutchings wrote: > On Fri, 2015-05-15 at 15:38 +0200, Willy Tarreau wrote: > > Hi Ben, > > > > On Fri, May 15, 2015 at 01:32:20PM +0100, Ben Hutchings wrote: > > > On Fri, 2015-05-15 at 10:05 +0200, Willy Tarreau wrote: > > > > 2.6.32-longterm review patch. If anyone has any objections, please let me know. > > > > > > > > ------------------ > > > > > > > > From: Andy Lutomirski <luto@xxxxxxxxxxxxxx> > > > > > > > > commit f647d7c155f069c1a068030255c300663516420e upstream. > > > > > > > > Otherwise, if buggy user code points DS or ES into the TLS > > > > array, they would be corrupted after a context switch. > > > > > > > > This also significantly improves the comments and documents some > > > > gotchas in the code. > > > > > > > > Before this patch, the both tests below failed. With this > > > > patch, the es test passes, although the gsbase test still fails. > > > [...] > > > > > > This depends on the changes to FPU/MMX/SSE state management that you > > > didn't apply to 2.6.32. Note this comment: > > > > > > /* Must be after DS reload */ > > > unlazy_fpu(prev_p); > > > > Are you sure you're not confusing with another one ? When running > > estest without this patch, I get "FAIL: ES corrupted 1000/1000 times" > > while I get "OK: ES was preserved" once applied, so it does seem to > > do what it's intended for. > > > > Also I'm not seeing any reference to the comment above in the patch > > nor around it, which leaves me confused :-/ > > v2.6.32.65:arch/x86/kernel/process_64.c:425: /* Must be after DS reload */ > > If this comment is correct then the patch will cause a regression for > FPU state management. The comment was introduced by: > > commit 0a5ace2ab08d45cd78d7ef0067cdcd5c812ac54f > Author: Andi Kleen <ak@xxxxxxx> > Date: Thu Oct 5 18:47:22 2006 +0200 > > [PATCH] x86-64: Fix FPU corruption And that replaced a longer comment that said "the AMD workaround requires it to be after DS reload". The comment above clear_fpu_state() says: /* AMD CPUs don't save/restore FDP/FIP/FOP unless an exception is pending. Clear the x87 state here by setting it to fixed values. The kernel data segment can be sometimes 0 and sometimes new user value. Both should be ok. Use the PDA as safe address because it should be already in L1. */ Hopefully Andi can explain further if needed; I have no idea. Ben. -- Ben Hutchings It is impossible to make anything foolproof because fools are so ingenious.
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