From 47a5c6fa0e204a2b63309c648bb2fde36836c826 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Mon, 18 Sep 2006 16:20:40 -0700 Subject: [PATCH] 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 Signed-off-by: Linus Torvalds --- arch/i386/kernel/entry.S | 4 ++++ include/asm-i386/system.h | 8 +++++++- 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S index 37a7d2eaf4..87f9f60b80 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 49928eb33f..098bcee94e 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), \ -- 2.39.5