linux-kernel - Re: [PATCH 5/6] x86: mass removal of ARGOFFSET

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Date:	Tue, 5 Aug 2014 13:09:48 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 5/6] x86: mass removal of ARGOFFSET

FYI: the patch is incomplete. arch/x86/ia32/ia32entry.S has a bug, fix is:

 sysexit_from_sys_call:
        andl    $~TS_COMPAT,TI_status+THREAD_INFO(%rsp,RIP-ARGOFFSET)
        /* clear IF, that popfq doesn't enable interrupts early */
-       andl  $~0x200,EFLAGS-R11(%rsp).
-       movl    RIP-R11(%rsp),%edx              /* User %eip */
+       andl    $~0x200,EFLAGS-ARGOFFSET(%rsp)
+       movl    RIP-ARGOFFSET(%rsp),%edx                /* User %eip */
        CFI_REGISTER rip,rdx
        RESTORE_ARGS 0,24,0,0,0,0
        xorq    %r8,%r8

It went unnoticed for so long because
these two constants are the same.
Patch #4 changes ARGOFFSET to 0, but of course R11 stays the same,
breaking this code.
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