Messages in this thread |  | | Date | Thu, 13 Nov 2014 02:43:20 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] x86: remove arbitrary instruction size limit in instruction decoder |
| |
On Wed, Nov 12, 2014 at 02:53:52PM -0800, Dave Hansen wrote: > We shouldn't simply error out when we get short copy_from_user*() > results from userspace (like intel_pmu_pebs_fixup_ip() does > currently). It is perfectly valid to be executing an instruction > within MAX_INSN_SIZE bytes of an unreadable page. We should be > able to gracefully handle short reads in those cases.
> diff -puN arch/x86/kernel/cpu/perf_event_intel_ds.c~x86-insn-decoder-remove-arbitrary-limit arch/x86/kernel/cpu/perf_event_intel_ds.c > --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c~x86-insn-decoder-remove-arbitrary-limit 2014-11-12 12:45:52.954753152 -0800 > +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c 2014-11-12 12:45:52.970753874 -0800
> @@ -758,11 +759,12 @@ static int intel_pmu_pebs_fixup_ip(struc > return 1; > } > > + size = ip - to; > if (!kernel_ip(ip)) { > - int size, bytes; > + int bytes; > u8 *buf = this_cpu_read(insn_buffer); > > - size = ip - to; /* Must fit our buffer, see above */ > + /* 'size' must fit our buffer, see above */ > bytes = copy_from_user_nmi(buf, (void __user *)to, size); > if (bytes != 0) > return 0;
Right, so we should better deal with short copies there. Should be doable.
|  |