[PATCH v4 06/27] x86/doublefault: Remove memmove() call

Peter Zijlstra
2020-02-21T13:50:38Z

Use of memmove() in #DF is problematic when you consider tracing and
other instrumentation.

Remove the memmove() call and simply write out what need doing; Boris
argues the ranges should not overlap.

Survives selftests/x86, specifically sigreturn_64.

(Andy ?!)

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200220121727.GB507@zn.tnic
---
arch/x86/kernel/traps.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -278,6 +278,7 @@ dotraplinkage void do_double_fault(struc
regs->ip == (unsigned long)native_irq_return_iret)
{
struct pt_regs *gpregs = (struct pt_regs *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
+ unsigned long *p = (unsigned long *)regs->sp;

/*
* regs->sp points to the failing IRET frame on the
@@ -285,7 +286,11 @@ dotraplinkage void do_double_fault(struc
* in gpregs->ss through gpregs->ip.
*
*/
- memmove(&gpregs->ip, (void *)regs->sp, 5*8);
+ gpregs->ip = p[0];
+ gpregs->cs = p[1];
+ gpregs->flags = p[2];
+ gpregs->sp = p[3];
+ gpregs->ss = p[4];
gpregs->orig_ax = 0; /* Missing (lost) #GP error code */

/*