From f2b375756c839ff655a3e0b45e339f8fbf973093 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 9 Mar 2016 19:00:30 -0800 Subject: x86/entry: Vastly simplify SYSENTER TF (single-step) handling Due to a blatant design error, SYSENTER doesn't clear TF (single-step). As a result, if a user does SYSENTER with TF set, we will single-step through the kernel until something clears TF. There is absolutely nothing we can do to prevent this short of turning off SYSENTER [1]. Simplify the handling considerably with two changes: 1. We already sanitize EFLAGS in SYSENTER to clear NT and AC. We can add TF to that list of flags to sanitize with no overhead whatsoever. 2. Teach do_debug() to ignore single-step traps in the SYSENTER prologue. That's all we need to do. Don't get too excited -- our handling is still buggy on 32-bit kernels. There's nothing wrong with the SYSENTER code itself, but the #DB prologue has a clever fixup for traps on the very first instruction of entry_SYSENTER_32, and the fixup doesn't work quite correctly. The next two patches will fix that. [1] We could probably prevent it by forcing BTF on at all times and making sure we clear TF before any branches in the SYSENTER code. Needless to say, this is a bad idea. Signed-off-by: Andy Lutomirski Cc: Andrew Cooper Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/a30d2ea06fe4b621fe6a9ef911b02c0f38feb6f2.1457578375.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/include/asm/proto.h | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) (limited to 'arch/x86/include/asm/proto.h') diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h index a4a77286cb1d..9b9b30b19441 100644 --- a/arch/x86/include/asm/proto.h +++ b/arch/x86/include/asm/proto.h @@ -7,12 +7,23 @@ void syscall_init(void); +#ifdef CONFIG_X86_64 void entry_SYSCALL_64(void); -void entry_SYSCALL_compat(void); +#endif + +#ifdef CONFIG_X86_32 void entry_INT80_32(void); -void entry_INT80_compat(void); void entry_SYSENTER_32(void); +void __begin_SYSENTER_singlestep_region(void); +void __end_SYSENTER_singlestep_region(void); +#endif + +#ifdef CONFIG_IA32_EMULATION void entry_SYSENTER_compat(void); +void __end_entry_SYSENTER_compat(void); +void entry_SYSCALL_compat(void); +void entry_INT80_compat(void); +#endif void x86_configure_nx(void); void x86_report_nx(void); -- cgit v1.2.3