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authorLinus Torvalds <torvalds@g5.osdl.org>2006-09-18 16:20:40 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-18 16:20:40 -0700
commit47a5c6fa0e204a2b63309c648bb2fde36836c826 (patch)
tree688b6c12c72fed720dc4a047f310cd292e88a6f1
parent1d19f176a2884d31c4fe2c7018349ff884a819b1 (diff)
x86: save/restore eflags in context switch
(And reset it on new thread creation) It turns out that eflags is important to save and restore not just because of iopl, but due to the magic bits like the NT bit, which we don't want leaking between different threads. Tested-by: Mike Galbraith <efault@gmx.de> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--arch/i386/kernel/entry.S4
-rw-r--r--include/asm-i386/system.h8
2 files changed, 11 insertions, 1 deletions
diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 37a7d2eaf4a0..87f9f60b803b 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -209,6 +209,10 @@ ENTRY(ret_from_fork)
GET_THREAD_INFO(%ebp)
popl %eax
CFI_ADJUST_CFA_OFFSET -4
+ pushl $0x0202 # Reset kernel eflags
+ CFI_ADJUST_CFA_OFFSET 4
+ popfl
+ CFI_ADJUST_CFA_OFFSET -4
jmp syscall_exit
CFI_ENDPROC
diff --git a/include/asm-i386/system.h b/include/asm-i386/system.h
index 49928eb33f8b..098bcee94e38 100644
--- a/include/asm-i386/system.h
+++ b/include/asm-i386/system.h
@@ -11,9 +11,14 @@
struct task_struct; /* one of the stranger aspects of C forward declarations.. */
extern struct task_struct * FASTCALL(__switch_to(struct task_struct *prev, struct task_struct *next));
+/*
+ * Saving eflags is important. It switches not only IOPL between tasks,
+ * it also protects other tasks from NT leaking through sysenter etc.
+ */
#define switch_to(prev,next,last) do { \
unsigned long esi,edi; \
- asm volatile("pushl %%ebp\n\t" \
+ asm volatile("pushfl\n\t" /* Save flags */ \
+ "pushl %%ebp\n\t" \
"movl %%esp,%0\n\t" /* save ESP */ \
"movl %5,%%esp\n\t" /* restore ESP */ \
"movl $1f,%1\n\t" /* save EIP */ \
@@ -21,6 +26,7 @@ extern struct task_struct * FASTCALL(__switch_to(struct task_struct *prev, struc
"jmp __switch_to\n" \
"1:\t" \
"popl %%ebp\n\t" \
+ "popfl" \
:"=m" (prev->thread.esp),"=m" (prev->thread.eip), \
"=a" (last),"=S" (esi),"=D" (edi) \
:"m" (next->thread.esp),"m" (next->thread.eip), \