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From: Denys Vlasenko <vda.linux@googlemail.com>
Date: Fri, 24 Apr 2015 01:22:46 +0200
Message-ID: <CAK1hOcNNvaoei-y_s1VgH2B5CVW=xMmZy5Tcx2sF8j-k8vUwNg@mail.gmail.com>
Subject: Re: [PATCH] x86/asm/entry/32: Restore %ss before SYSRETL if necessary
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>, "H. Peter Anvin" <hpa@zytor.com>,
        Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, Ingo Molnar <mingo@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>, Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Apr 24, 2015 at 1:04 AM, Linus Torvalds
<torvalds@linux-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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