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x86_64, traps: Fix the espfix64 #DF fixup and rewrite it in C

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There's nothing special enough about the espfix64 double fault fixup to
justify writing it in assembly.  Move it to C.

This also fixes a bug: if the double fault came from an IST stack, the
old asm code would return to a partially uninitialized stack frame.

Fixes: 3891a04aaf
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andy Lutomirski
2014-11-22 18:00:31 -08:00
committed by Linus Torvalds
parent fc14f9c127
commit af726f21ed
2 changed files with 26 additions and 32 deletions
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24
arch/x86/kernel/traps.c
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@@ -259,6 +259,30 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
static const char str[] = "double fault";
struct task_struct *tsk = current;
#ifdef CONFIG_X86_ESPFIX64
extern unsigned char native_irq_return_iret[];
/*
* If IRET takes a non-IST fault on the espfix64 stack, then we
* end up promoting it to a doublefault. In that case, modify
* the stack to make it look like we just entered the #GP
* handler from user space, similar to bad_iret.
*/
if (((long)regs->sp >> PGDIR_SHIFT) == ESPFIX_PGD_ENTRY &&
regs->cs == __KERNEL_CS &&
regs->ip == (unsigned long)native_irq_return_iret)
{
struct pt_regs *normal_regs = task_pt_regs(current);
/* Fake a #GP(0) from userspace. */
memmove(&normal_regs->ip, (void *)regs->sp, 5*8);
normal_regs->orig_ax = 0; /* Missing (lost) #GP error code */
regs->ip = (unsigned long)general_protection;
regs->sp = (unsigned long)&normal_regs->orig_ax;
return;
}
#endif
exception_enter();
/* Return not checked because double check cannot be ignored */
notify_die(DIE_TRAP, str, regs, error_code, X86_TRAP_DF, SIGSEGV);