linux-kernel - Re: [PATCH] x86/asm/entry/32: Restore %ss before SYSRETL if necessary

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Message-ID: <CAK1hOcNNvaoei-y_s1VgH2B5CVW=xMmZy5Tcx2sF8j-k8vUwNg@mail.gmail.com>
Date:	Fri, 24 Apr 2015 01:22:46 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/asm/entry/32: Restore %ss before SYSRETL if necessary

On Fri, Apr 24, 2015 at 1:04 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> And at that point,> the only cost is a a single no-op on most CPU's (we still don't know
> _which_ AMD CPU's are affected, but I guess we could start off with
> all of them and see if we can get an exhaustive list some way).

This seems to be "architectural" for AMD CPU's, similar to Intel's
SYSRET bug with non-canonical return address. Meaning,
both bugs, are documented by respective
companies. Both are officially "not a bug, but a feature".
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