[PATCH v3 04/22] x86/doublefault: Make memmove() notrace/NOKPROBE

Peter Zijlstra
2020-02-19T15:15:12Z

Hitting the tracer or a kprobes from #DF is 'interesting', lets avoid
that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/traps.c | 3 ++-
arch/x86/lib/memcpy_32.c | 7 ++++++-
arch/x86/lib/memmove_64.S | 5 +++++
3 files changed, 13 insertions(+), 2 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -271,7 +271,8 @@ dotraplinkage void do_double_fault(struc
* The net result is that our #GP handler will think that we
* entered from usermode with the bad user context.
*
- * No need for nmi_enter() here because we don't use RCU.
+ * No need for nmi_enter() here because we don't call out to anything
+ * except memmove() and that is notrace/NOKPROBE.
*/
if (((long)regs->sp >> P4D_SHIFT) == ESPFIX_PGD_ENTRY &&
regs->cs == __KERNEL_CS &&
--- a/arch/x86/lib/memcpy_32.c
+++ b/arch/x86/lib/memcpy_32.c
@@ -21,7 +21,7 @@ __visible void *memset(void *s, int c, s
}
EXPORT_SYMBOL(memset);

-__visible void *memmove(void *dest, const void *src, size_t n)
+__visible notrace void *memmove(void *dest, const void *src, size_t n)
{
int d0,d1,d2,d3,d4,d5;
char *ret = dest;
@@ -207,3 +207,8 @@ __visible void *memmove(void *dest, cons

}
EXPORT_SYMBOL(memmove);
+/*
+ * The double fault handler uses memmove(), do not mess with it or risk a
+ * tripple fault.
+ */
+NOKPROBE_SYMBOL(memmove);
--- a/arch/x86/lib/memmove_64.S
+++ b/arch/x86/lib/memmove_64.S
@@ -212,3 +212,8 @@ SYM_FUNC_END(__memmove)
SYM_FUNC_END_ALIAS(memmove)
EXPORT_SYMBOL(__memmove)
EXPORT_SYMBOL(memmove)
+/*
+ * The double fault handler uses memmove(), do not mess with it or risk a
+ * tripple fault.
+ */
+_ASM_NOKPROBE(__memmove)