From 1cf8343f55525c09c88da0a494a96e1b034f84e2 Mon Sep 17 00:00:00 2001 From: Seiichi Ikarashi Date: Tue, 6 Dec 2011 17:58:14 +0900 Subject: [PATCH] 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 Tested-by: Masayoshi MIZUMA Cc: Jan Beulich Cc: Frederic Weisbecker Cc: Linus Torvalds Signed-off-by: Ingo Molnar --- arch/x86/include/asm/processor-flags.h | 1 + arch/x86/kernel/entry_64.S | 2 +- arch/x86/kernel/process.c | 2 +- drivers/lguest/x86/core.c | 2 +- 4 files changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/processor-flags.h b/arch/x86/include/asm/processor-flags.h index 2dddb317bb39..f8ab3eaad128 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 cfad7fce6163..a20e1cb9dc87 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -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*/ diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index ee5d4fbd53b4..15763af7bfe3 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -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, ®s, 0, NULL, NULL); diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c index 65af42f2d593..39809035320a 100644 --- a/drivers/lguest/x86/core.c +++ b/drivers/lguest/x86/core.c @@ -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 -- 2.20.1