Commit-ID: 2a41aa4feb25af3ead60b740c43df80c576efea2 Gitweb: http://git.kernel.org/tip/2a41aa4feb25af3ead60b740c43df80c576efea2 Author: Andy Lutomirski <[email protected]> AuthorDate: Wed, 9 Mar 2016 19:00:33 -0800 Committer: Ingo Molnar <[email protected]> CommitDate: Thu, 10 Mar 2016 09:48:14 +0100
x86/entry/32: Add and check a stack canary for the SYSENTER stack The first instruction of the SYSENTER entry runs on its own tiny stack. That stack can be used if a #DB or NMI is delivered before the SYSENTER prologue switches to a real stack. We have code in place to prevent us from overflowing the tiny stack. For added paranoia, add a canary to the stack and check it in do_debug() -- that way, if something goes wrong with the #DB logic, we'll eventually notice. Signed-off-by: Andy Lutomirski <[email protected]> Cc: Andrew Cooper <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/6ff9a806f39098b166dc2c41c1db744df5272f29.1457578375.git.l...@kernel.org Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/include/asm/processor.h | 3 ++- arch/x86/kernel/process.c | 3 +++ arch/x86/kernel/traps.c | 8 ++++++++ 3 files changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index 7cd01b7..50a6dc8 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -299,8 +299,9 @@ struct tss_struct { #ifdef CONFIG_X86_32 /* - * Space for the temporary SYSENTER stack: + * Space for the temporary SYSENTER stack. */ + unsigned long SYSENTER_stack_canary; unsigned long SYSENTER_stack[64]; #endif diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 9f7c21c..ee9a979 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -57,6 +57,9 @@ __visible DEFINE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss) = { */ .io_bitmap = { [0 ... IO_BITMAP_LONGS] = ~0 }, #endif +#ifdef CONFIG_X86_32 + .SYSENTER_stack_canary = STACK_END_MAGIC, +#endif }; EXPORT_PER_CPU_SYMBOL(cpu_tss); diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index b0ddb819..49e2e77 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -713,6 +713,14 @@ dotraplinkage void do_debug(struct pt_regs *regs, long error_code) debug_stack_usage_dec(); exit: +#if defined(CONFIG_X86_32) + /* + * This is the most likely code path that involves non-trivial use + * of the SYSENTER stack. Check that we haven't overrun it. + */ + WARN(this_cpu_read(cpu_tss.SYSENTER_stack_canary) != STACK_END_MAGIC, + "Overran or corrupted SYSENTER stack\n"); +#endif ist_exit(regs); } NOKPROBE_SYMBOL(do_debug);
