x86: Fix rflags in FAKE_STACK_FRAME
The x86_64 kernel pushes the fake kernel stack in
arch/x86/kernel/entry_64.S:FAKE_STACK_FRAME, and
rflags register in it does not conform to the specification.
Although Intel's manual[1] says bit 1 of it shall be set to 1,
this bit is cleared to 0 on pushing the fake stack.
[1] Intel(R) 64 and IA-32 Architectures Software Developer's Manual
Vol.1 3-21 Figure 3-8. EFLAGS Register
If it is not on purpose, it is better to be fixed, because
it can lead some tools misunderstanding the stack frame. For example,
"crash" utility[2] actually detects it and warns you like
below:
RIP: ffffffff8005dfa2 RSP: ffff8104ce0c7f58 RFLAGS: 00000200
[...]
bt: WARNING: possibly bogus exception frame
Signed-off-by: Seiichi Ikarashi <s.ikarashi@jp.fujitsu.com>
Tested-by: Masayoshi MIZUMA <m.mizuma@jp.fujitsu.com>
Cc: Jan Beulich <JBeulich@suse.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/include/asm/processor-flags.h b/arch/x86/include/asm/processor-flags.h
index 2dddb31..f8ab3ea 100644
--- a/arch/x86/include/asm/processor-flags.h
+++ b/arch/x86/include/asm/processor-flags.h
@@ -6,6 +6,7 @@
* EFLAGS bits
*/
#define X86_EFLAGS_CF 0x00000001 /* Carry Flag */
+#define X86_EFLAGS_BIT1 0x00000002 /* Bit 1 - always on */
#define X86_EFLAGS_PF 0x00000004 /* Parity Flag */
#define X86_EFLAGS_AF 0x00000010 /* Auxiliary carry Flag */
#define X86_EFLAGS_ZF 0x00000040 /* Zero Flag */
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index cfad7fce..a20e1cb 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -221,7 +221,7 @@
/*CFI_REL_OFFSET ss,0*/
pushq_cfi %rax /* rsp */
CFI_REL_OFFSET rsp,0
- pushq_cfi $X86_EFLAGS_IF /* eflags - interrupts on */
+ pushq_cfi $(X86_EFLAGS_IF|X86_EFLAGS_BIT1) /* eflags - interrupts on */
/*CFI_REL_OFFSET rflags,0*/
pushq_cfi $__KERNEL_CS /* cs */
/*CFI_REL_OFFSET cs,0*/
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index ee5d4fb..15763af 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -293,7 +293,7 @@
regs.orig_ax = -1;
regs.ip = (unsigned long) kernel_thread_helper;
regs.cs = __KERNEL_CS | get_kernel_rpl();
- regs.flags = X86_EFLAGS_IF | 0x2;
+ regs.flags = X86_EFLAGS_IF | X86_EFLAGS_BIT1;
/* Ok, create the new process.. */
return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, ®s, 0, NULL, NULL);
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index 65af42f..39809035 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -697,7 +697,7 @@
* interrupts are enabled. We always leave interrupts enabled while
* running the Guest.
*/
- regs->eflags = X86_EFLAGS_IF | 0x2;
+ regs->eflags = X86_EFLAGS_IF | X86_EFLAGS_BIT1;
/*
* The "Extended Instruction Pointer" register says where the Guest is