Before the patch, tss.stack field was not referenced anywhere. It was used only by setting sysenter's stack to point after last byte of tss, thus the trailing field, stack[64], was used. But grep would not know it. You can comment it out, compile, and kernel will even run until an unlucky NMI corrupts iomap[] (which is also not easily detectable).
This patch changes code so the purpose and usage of this field is not mysterious anymore, and can be easily grepped for. This does change generated code, for a subtle reason: since tss_struct is ____cacheline_aligned, there happen to be 5 longs of padding at the end. Old code was using the padding too; new code will strictly use only SYSENTER_stack[]. Signed-off-by: Denys Vlasenko <[email protected]> CC: Linus Torvalds <[email protected]> CC: Steven Rostedt <[email protected]> CC: Ingo Molnar <[email protected]> CC: Borislav Petkov <[email protected]> CC: "H. Peter Anvin" <[email protected]> CC: Andy Lutomirski <[email protected]> CC: Oleg Nesterov <[email protected]> CC: Frederic Weisbecker <[email protected]> CC: Alexei Starovoitov <[email protected]> CC: Will Drewry <[email protected]> CC: Kees Cook <[email protected]> CC: [email protected] CC: [email protected] --- arch/x86/include/asm/processor.h | 5 +++-- arch/x86/kernel/asm-offsets_32.c | 2 +- arch/x86/kernel/cpu/common.c | 2 +- 3 files changed, 5 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 48a61c1..4172241 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -276,9 +276,10 @@ struct tss_struct { unsigned long io_bitmap[IO_BITMAP_LONGS + 1]; /* - * .. and then another 0x100 bytes for the emergency kernel stack: + * and then space for temporary SYSENTER stack: */ - unsigned long stack[64]; + unsigned long SYSENTER_stack[63]; + unsigned long SYSENTER_stack_last_word; } ____cacheline_aligned; diff --git a/arch/x86/kernel/asm-offsets_32.c b/arch/x86/kernel/asm-offsets_32.c index 3b3b9d3..4a3cbd0 100644 --- a/arch/x86/kernel/asm-offsets_32.c +++ b/arch/x86/kernel/asm-offsets_32.c @@ -68,7 +68,7 @@ void foo(void) /* Offset from the sysenter stack to tss.sp0 */ DEFINE(TSS_sysenter_sp0, offsetof(struct tss_struct, x86_tss.sp0) - - sizeof(struct tss_struct)); + (offsetof(struct tss_struct, SYSENTER_stack_last_word) + 4)); #if defined(CONFIG_LGUEST) || defined(CONFIG_LGUEST_GUEST) || defined(CONFIG_LGUEST_MODULE) BLANK(); diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 7634833..8180e0b 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -987,7 +987,7 @@ void enable_sep_cpu(void) } tss->x86_tss.ss1 = __KERNEL_CS; - tss->x86_tss.sp1 = sizeof(struct tss_struct) + (unsigned long) tss; + tss->x86_tss.sp1 = ((unsigned long) &tss->SYSENTER_stack_last_word) + 4; wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0); wrmsr(MSR_IA32_SYSENTER_ESP, tss->x86_tss.sp1, 0); wrmsr(MSR_IA32_SYSENTER_EIP, (unsigned long) ia32_sysenter_target, 0); -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
