[tip: x86/entry] x86/traps: Mark fixup_bad_iret() noinstr

tip-bot2 for Thomas Gleixner
2020-05-19T20:00:24Z

The following commit has been merged into the x86/entry branch of tip:

Commit-ID: 68a05c6247d2aa67f5ada1009ffd19758e5914ea
Gitweb: https://git.kernel.org/tip/68a05c6247d2aa67f5ada1009ffd19758e5914ea
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Wed, 25 Mar 2020 19:53:38 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 19 May 2020 16:03:52 +02:00

x86/traps: Mark fixup_bad_iret() noinstr

This is called from deep entry ASM in a situation where instrumentation
will cause more harm than providing useful information.

Switch from memmove() to memcpy() because memmove() can't be called
from noinstr code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505134903.346741553@linutronix.de

---
arch/x86/kernel/traps.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 48468f6..b2b3656 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -578,7 +578,7 @@ struct bad_iret_stack {
struct pt_regs regs;
};

-asmlinkage __visible notrace
+asmlinkage __visible noinstr
struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
{
/*
@@ -589,19 +589,21 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
* just below the IRET frame) and we want to pretend that the
* exception came from the IRET target.
*/
- struct bad_iret_stack *new_stack =
- (struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
+ struct bad_iret_stack tmp, *new_stack =
+ (struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;

- /* Copy the IRET target to the new stack. */
- memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
+ /* Copy the IRET target to the temporary storage. */
+ memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);

/* Copy the remainder of the stack from the current stack. */
- memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
+ memcpy(&tmp, s, offsetof(struct bad_iret_stack, regs.ip));
+
+ /* Update the entry stack */
+ memcpy(new_stack, &tmp, sizeof(tmp));

BUG_ON(!user_mode(&new_stack->regs));
return new_stack;
}
-NOKPROBE_SYMBOL(fixup_bad_iret);
#endif

static bool is_sysenter_singlestep(struct pt_regs *regs)