Messages in this thread | | | From | Jann Horn <> | Date | Thu, 4 Apr 2019 18:31:37 +0200 | Subject | Re: [PATCH] x86/microcode: Refactor Intel microcode loading |
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On Thu, Apr 4, 2019 at 6:28 PM Borislav Petkov <bp@alien8.de> wrote: > > On Thu, Apr 04, 2019 at 01:11:28PM +0200, Jann Horn wrote: > > This changes generic_load_microcode() to use the iov_iter API instead of > > an open-coded version. This allows us to avoid explicitly casting between > > user and kernel pointers. > > > > Because the iov_iter API makes it hard to read the same location twice, as > > a side effect, this also fixes a double-read of the microcode header (which > > could e.g. lead to out-of-bounds reads in microcode_sanity_check()). > > Not that it matters much, only root can do this anyway... > > > > Signed-off-by: Jann Horn <jannh@google.com> > > --- > > I have tested that with this patch applied, microcode loading still works > > both via "iucode-tool -k" and via > > /sys/devices/system/cpu/microcode/reload. > > Yeah, this cannot have worked because I think I broke it recently and > you'd need this:
Uuuh. I *definitely* tested this. I ran this yesterday evening on my home machine, on top of commit 14c741de93861749dfb60b4964028541f5c506ca from Linus' tree, plus two cherry-picked fixes for drm/ttm. I specifically made sure that I had the old microcode version before reloading these ways and I had the new version after reloading. And the verbose dmesg logs also looked okay.
> --- > diff --git a/arch/x86/kernel/cpu/microcode/core.c b/arch/x86/kernel/cpu/microcode/core.c > index 5260185cbf7b..8a4a7823451a 100644 > --- a/arch/x86/kernel/cpu/microcode/core.c > +++ b/arch/x86/kernel/cpu/microcode/core.c > @@ -418,8 +418,9 @@ static int do_microcode_update(const void __user *buf, size_t size) > if (ustate == UCODE_ERROR) { > error = -1; > break; > - } else if (ustate == UCODE_OK) > + } else if (ustate == UCODE_NEW) { > apply_microcode_on_target(cpu); > + } > } > > return error; > --- > > Regardless, I'll take care of it. Thanks a lot for doing this cleanup, > it looks really cool and nicely clean - exactly how I envisioned it. :-) > > I'll test it more later with the above fix and apply it. > > Thx. > > -- > Regards/Gruss, > Boris. > > Good mailing practices for 400: avoid top-posting and trim the reply.
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