[tip:x86/urgent] x86/entry/64: Fix context tracking state warning when load_gs_index fails

From: tip-bot for Wanpeng Li
Date: Fri Sep 30 2016 - 08:08:15 EST

Commit-ID: 2fa5f04f85730d0c4f49f984b7efeb4f8d5bd1fc
Gitweb: http://git.kernel.org/tip/2fa5f04f85730d0c4f49f984b7efeb4f8d5bd1fc
Author: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
AuthorDate: Fri, 30 Sep 2016 09:01:06 +0800
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 30 Sep 2016 13:53:12 +0200

x86/entry/64: Fix context tracking state warning when load_gs_index fails

This warning:

WARNING: CPU: 0 PID: 3331 at arch/x86/entry/common.c:45 enter_from_user_mode+0x32/0x50
CPU: 0 PID: 3331 Comm: ldt_gdt_64 Not tainted 4.8.0-rc7+ #13
Call Trace:
? general_protection+0x12/0x30
? native_load_gs_index+0xd/0x20
? do_set_thread_area+0x19c/0x1f0

... can be reproduced by running the GS testcase of the ldt_gdt test unit in
the x86 selftests.

do_int80_syscall_32() will call enter_form_user_mode() to convert context
tracking state from user state to kernel state. The load_gs_index() call
can fail with user gsbase, gsbase will be fixed up and proceed if this

However, enter_from_user_mode() will be called again in the fixed up path
though it is context tracking kernel state currently.

This patch fixes it by just fixing up gsbase and telling lockdep that IRQs
are off once load_gs_index() failed with user gsbase.

Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Acked-by: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1475197266-3440-1-git-send-email-wanpeng.li@xxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
arch/x86/entry/entry_64.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d172c61..02fff3e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1002,7 +1002,6 @@ ENTRY(error_entry)
testb $3, CS+8(%rsp)
jz .Lerror_kernelspace

* We entered from user mode or we're pretending to have entered
* from user mode due to an IRET fault.
@@ -1045,7 +1044,8 @@ ENTRY(error_entry)
* gsbase and proceed. We'll fix up the exception and land in
* .Lgs_change's error handler with kernel gsbase.
- jmp .Lerror_entry_from_usermode_swapgs
+ jmp .Lerror_entry_done

/* Fix truncated RIP */