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Commit 1cf8343f authored by Seiichi Ikarashi's avatar Seiichi Ikarashi Committed by Ingo Molnar
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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: default avatarSeiichi Ikarashi <s.ikarashi@jp.fujitsu.com>
Tested-by: default avatarMasayoshi 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: default avatarIngo Molnar <mingo@elte.hu>
parent cc3a1bf5

arch/x86/include/asm/processor-flags.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */

arch/x86/kernel/entry_64.S

+1 −1
Original line number Diff line number Diff line
@@ -221,7 +221,7 @@ ENDPROC(native_usergs_sysret64) 
	/*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*/

arch/x86/kernel/process.c

+1 −1
Original line number Diff line number Diff line
@@ -293,7 +293,7 @@ int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags) 
	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, &regs, 0, NULL, NULL);

drivers/lguest/x86/core.c

+1 −1
Original line number Diff line number Diff line
@@ -697,7 +697,7 @@ void lguest_arch_setup_regs(struct lg_cpu *cpu, unsigned long start) 
	 * 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