linux-kernel - [PATCH] x86/asm/entry/32: Reinstate clearing of pt

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Message-Id: <1433701470-28800-1-git-send-email-dvlasenk@redhat.com>
Date:	Sun,  7 Jun 2015 20:24:30 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>,
	"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: [PATCH] x86/asm/entry/32: Reinstate clearing of pt_regs->r8..r11 on EFAULT path

I broke this recently when I changed pt_regs->r8..r11 clearing logic
in INT 80 code path.

There is a branch from SYSENTER/SYSCALL code to INT 80 code:
if we fail to retrieve arg6, we return EFAULT. Before this patch,
in this case we don't clear pt_regs->r8..r11.

This patch fixes this. The resulting code is smaller and simpler.

While at it, remove incorrect comment about syscall dispatching CALL insn:
it does not use RIP-relative addressing form (the comment was meant to be
"TODO: make this rip-relative", and morphed since then, dropping "TODO").

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
---
 arch/x86/entry/entry_64_compat.S | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 9558dac..b80f8d4 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -413,9 +413,7 @@ END(ia32_cstar_target)
 
 ia32_badarg:
 	ASM_CLAC
-	movq	$-EFAULT, %rax
-	jmp	ia32_sysret
-
+	movq	$-EFAULT, RAX(%rsp)
 ia32_ret_from_sys_call:
 	xorl	%eax, %eax		/* Do not leak kernel information */
 	movq	%rax, R11(%rsp)
@@ -486,9 +484,7 @@ ia32_do_call:
 	cmpq	$(IA32_NR_syscalls-1), %rax
 	ja	1f
 
-	call	*ia32_sys_call_table(, %rax, 8) /* RIP relative */
-
-ia32_sysret:
+	call	*ia32_sys_call_table(, %rax, 8)
 	movq	%rax, RAX(%rsp)
 1:
 	jmp	int_ret_from_sys_call
-- 
1.8.1.4

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