linux-kernel - Re: [PATCH 1/2 v2] x86/asm/entry/64: better label name, fix comments

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Date:	Thu, 26 Mar 2015 12:45:39 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	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>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 v2] x86/asm/entry/64: better label name, fix comments

On Wed, Mar 25, 2015 at 07:20:28PM +0100, Denys Vlasenko wrote:
> A named label "ret_from_sys_call" implies that there are jumps
> to this location from elsewhere, as happens with many other labels
> in this file.
> But this label is used only by the JMP a few insns above.
> To make that obvious, use local numeric label instead.
> 
> Do the same in the second copy of the syscall table dispatch code,
> it has a similar JMP which skips the CALL.
> 
> Improve comments:
> 
> "and return regs->ax" isn't too informative. We always return regs->ax.
> 
> The comment suggesting that it'd be cool to use rip relative addressing for CALL
> is deleted. It's unclear why that would be an improvement - we aren't striving
> to use position-independent code here. PIC code here would require something like
> LEA sys_call_table(%rip),reg + CALL *(reg,%rax*8)...
> 
> "iret frame is also incomplete" is no longer true, fix that too.
> 
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: Ingo Molnar <mingo@...nel.org>
> CC: Borislav Petkov <bp@...en8.de>
> CC: "H. Peter Anvin" <hpa@...or.com>
> CC: Andy Lutomirski <luto@...capital.net>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: Frederic Weisbecker <fweisbec@...il.com>
> CC: Alexei Starovoitov <ast@...mgrid.com>
> CC: Will Drewry <wad@...omium.org>
> CC: Kees Cook <keescook@...omium.org>
> CC: x86@...nel.org
> CC: linux-kernel@...r.kernel.org
> ---
> 
> Changes in v2: gave "jmp 1f" treatment to the second jump.
> 
>  arch/x86/kernel/entry_64.S | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)

Acked-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

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