[PATCH] x86/retpoline: Remove the esp/rsp thunk

[PATCH] x86/retpoline: Remove the esp/rsp thunk

[Waiman Long]

It doesn't make sense to have an indirect call thunk with esp/rsp as
retpoline code won't work correctly with the stack pointer register.
Removing it will help compiler writers to catch error in case such
a thunk call is emitted incorrectly.

Fixes: 76b043848fd2 ("x86/retpoline: Add initial retpoline support")
Suggested-by: Jeff Law <law@redhat.com>
Signed-off-by: Waiman Long <longman@redhat.com>
---
 arch/x86/include/asm/asm-prototypes.h | 1 -
 arch/x86/lib/retpoline.S              | 1 -
 2 files changed, 2 deletions(-)

diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index 0927cdc..1908214 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -38,5 +38,4 @@
 INDIRECT_THUNK(si)
 INDIRECT_THUNK(di)
 INDIRECT_THUNK(bp)
-INDIRECT_THUNK(sp)
 #endif /* CONFIG_RETPOLINE */
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index dfb2ba9..c909961 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -36,7 +36,6 @@ GENERATE_THUNK(_ASM_DX)
 GENERATE_THUNK(_ASM_SI)
 GENERATE_THUNK(_ASM_DI)
 GENERATE_THUNK(_ASM_BP)
-GENERATE_THUNK(_ASM_SP)
 #ifdef CONFIG_64BIT
 GENERATE_THUNK(r8)
 GENERATE_THUNK(r9)
-- 
1.8.3.1

Re: [PATCH] x86/retpoline: Remove the esp/rsp thunk

[David Woodhouse]

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On Mon, 2018-01-22 at 17:09 -0500, Waiman Long wrote:
> It doesn't make sense to have an indirect call thunk with esp/rsp as
> retpoline code won't work correctly with the stack pointer register.
> Removing it will help compiler writers to catch error in case such
> a thunk call is emitted incorrectly.
> 
> Fixes: 76b043848fd2 ("x86/retpoline: Add initial retpoline support")
> Suggested-by: Jeff Law <law@redhat.com>
> Signed-off-by: Waiman Long <longman@redhat.com>

Acked-by: David Woodhouse <dwmw@amazon.co.uk>

I spotted that and *almost* removed it a couple of times in other
refactoring, but after abandoning those I forgot to come back and do
just this. Thanks.

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[tip:x86/pti] x86/retpoline: Remove the esp/rsp thunk

[tip-bot for Waiman Long]

Commit-ID:  1df37383a8aeabb9b418698f0bcdffea01f4b1b2
Gitweb:     https://git.kernel.org/tip/1df37383a8aeabb9b418698f0bcdffea01f4b1b2
Author:     Waiman Long <longman@redhat.com>
AuthorDate: Mon, 22 Jan 2018 17:09:34 -0500
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 24 Jan 2018 12:31:55 +0100

x86/retpoline: Remove the esp/rsp thunk

It doesn't make sense to have an indirect call thunk with esp/rsp as
retpoline code won't work correctly with the stack pointer register.
Removing it will help compiler writers to catch error in case such
a thunk call is emitted incorrectly.

Fixes: 76b043848fd2 ("x86/retpoline: Add initial retpoline support")
Suggested-by: Jeff Law <law@redhat.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Woodhouse <dwmw@amazon.co.uk>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Kees Cook <keescook@google.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linux-foundation.org>
Cc: Paul Turner <pjt@google.com>
Link: https://lkml.kernel.org/r/1516658974-27852-1-git-send-email-longman@redhat.com

---
 arch/x86/include/asm/asm-prototypes.h | 1 -
 arch/x86/lib/retpoline.S              | 1 -
 2 files changed, 2 deletions(-)

diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index 0927cdc..1908214 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -38,5 +38,4 @@ INDIRECT_THUNK(dx)
 INDIRECT_THUNK(si)
 INDIRECT_THUNK(di)
 INDIRECT_THUNK(bp)
-INDIRECT_THUNK(sp)
 #endif /* CONFIG_RETPOLINE */
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index dfb2ba9..c909961 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -36,7 +36,6 @@ GENERATE_THUNK(_ASM_DX)
 GENERATE_THUNK(_ASM_SI)
 GENERATE_THUNK(_ASM_DI)
 GENERATE_THUNK(_ASM_BP)
-GENERATE_THUNK(_ASM_SP)
 #ifdef CONFIG_64BIT
 GENERATE_THUNK(r8)
 GENERATE_THUNK(r9)