linux-kernel - Re: [PATCH 3/5] x86/asm/entry/32: Jump from SYSENTER32 to SYSCALL32 code path

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Date:	Mon, 27 Jul 2015 15:37:34 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Krzysztof A. Sobiecki" <sobkas@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, 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 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] x86/asm/entry/32: Jump from SYSENTER32 to SYSCALL32
 code path

> Subject: [PATCH 3/5] x86/asm/entry/32: Jump from SYSENTER32 to SYSCALL32 code path

Shouldn't that be /64, not /32, or maybe /64/compat?

On Mon, Jul 27, 2015 at 1:33 PM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
> In 32-bit SYSENTER code, load arg6 into R9 instead of EBP.
> Jump to SYSCALL code path after we finish setting up pt_regs
> and clearing FLAGS_NT.
>
> This leaves most of SYSENTER32 code path inaccessible.
>
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Ingo Molnar <mingo@...nel.org>
> CC: Linus Torvalds <torvalds@...ux-foundation.org>
> CC: Krzysztof A. Sobiecki <sobkas@...il.com>
> CC: Steven Rostedt <rostedt@...dmis.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
> ---
>  arch/x86/entry/entry_64_compat.S | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
> index df102e8..d74745a 100644
> --- a/arch/x86/entry/entry_64_compat.S
> +++ b/arch/x86/entry/entry_64_compat.S
> @@ -93,7 +93,7 @@ ENTRY(entry_SYSENTER_compat)
>          * 32-bit zero extended
>          */
>         ASM_STAC
> -1:     movl    (%rbp), %ebp
> +1:     movl    (%rbp), %r9d

You're sticking arg6 into r9d here, I think, and then:


>
>         orl     $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
>         testl   $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
> @@ -343,6 +344,7 @@ ENTRY(entry_SYSCALL_compat)
>         _ASM_EXTABLE(1b, ia32_badarg)
>         ASM_CLAC
>
> +sysenter_jumps_here:
>         orl     $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
>         testl   $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
>         jnz     cstar_tracesys

you land here, which eventually does:

    movl    %ebp, %r9d        /* arg6 */

What am I missing?

--Andy
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