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Commit 47a5c6fa authored by Linus Torvalds's avatar Linus Torvalds
Browse files

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: default avatarMike Galbraith <efault@gmx.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 1d19f176

arch/i386/kernel/entry.S

+4 −0
Original line number Diff line number Diff line
@@ -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

include/asm-i386/system.h

+7 −1
Original line number Diff line number Diff line
@@ -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),	\