Commit-ID: 2a41aa4feb25af3ead60b740c43df80c576efea2
Gitweb: http://git.kernel.org/tip/2a41aa4feb25af3ead60b740c43df80c576efea2
Author: Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Wed, 9 Mar 2016 19:00:33 -0800
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
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 <luto@xxxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/6ff9a806f39098b166dc2c41c1db744df5272f29.1457578375.git.luto@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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);
--
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