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

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Message-ID: <20150423214616.GU28327@pd.tnic>
Date:	Thu, 23 Apr 2015 23:46:16 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Thu, Apr 23, 2015 at 02:37:27PM -0700, H. Peter Anvin wrote:
> Yes, the NULL SS is a special thing in 64-bit mode. I agree that
> context-switching it is probably the way to go; it should be cheap
> enough. We might even be able to conditionalize it on an X86_BUG_
> flag.

Oh sure, I was thinking of an AMD-specific

	"call amd_fixup_ss"

which gets NOPped out on Intel.

We do those for breakfast :-)

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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