[PATCH v2] x86/entry/64: Fix context tracking state warning when load_gs_index fails

From: Wanpeng Li
Date: Thu Sep 29 2016 - 21:01:21 EST

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

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

This can be reproduced by running the GS testcase of ldt_gdt test unit in

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 can fail
with user gsbase, gsbase will be fixed up and proceed if this happen.
However, enter_from_user_mode() will be called again in the fixed up path
though it is context tracking kernel state currently.

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

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
v1 -> v2:
* more readable

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 */