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SubjectRe: [PATCH] x86/microcode: Refactor Intel microcode loading
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:

---
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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