3.16.56-rc1 review patch. If anyone has any objections, please let me know.
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From: Thomas Gleixner tglx@linutronix.de
commit 66c117d7fa2ae429911e60d84bf31a90b2b96189 upstream.
Richard reported the following crash:
[ 0.036000] BUG: unable to handle kernel paging request at 55501e06 [ 0.036000] IP: [<c0aae48b>] common_interrupt+0xb/0x38 [ 0.036000] Call Trace: [ 0.036000] [<c0409c80>] ? add_nops+0x90/0xa0 [ 0.036000] [<c040a054>] apply_alternatives+0x274/0x630
Chuck decoded:
" 0: 8d 90 90 83 04 24 lea 0x24048390(%eax),%edx 6: 80 fc 0f cmp $0xf,%ah 9: a8 0f test $0xf,%al
b: a0 06 1e 50 55 mov 0x55501e06,%al
10: 57 push %edi 11: 56 push %esi
Interrupt 0x30 occurred while the alternatives code was replacing the initial 0x90,0x90,0x90 NOPs (from the ASM_CLAC macro) with the optimized version, 0x8d,0x76,0x00. Only the first byte has been replaced so far, and it makes a mess out of the insn decoding."
optimize_nops() is buggy in two aspects:
- It's not disabling interrupts across the modification - It's lacking a sync_core() call
Add both.
Fixes: 4fd4b6e5537c 'x86/alternatives: Use optimized NOPs for padding' Reported-and-tested-by: "Richard W.M. Jones" rjones@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Richard W.M. Jones rjones@redhat.com Cc: Chuck Ebbert cebbert.lkml@gmail.com Cc: Borislav Petkov bp@alien8.de Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1509031232340.15006@nanos Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/x86/kernel/alternative.c | 5 +++++ 1 file changed, 5 insertions(+)
--- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -325,10 +325,15 @@ done:
static void __init_or_module optimize_nops(struct alt_instr *a, u8 *instr) { + unsigned long flags; + if (instr[0] != 0x90) return;
+ local_irq_save(flags); add_nops(instr + (a->instrlen - a->padlen), a->padlen); + sync_core(); + local_irq_restore(flags);
DUMP_BYTES(instr, a->instrlen, "%p: [%d:%d) optimized NOPs: ", instr, a->instrlen - a->padlen, a->padlen);