On Mon, Sep 20, 2021 at 06:17:36PM +0200, Fabio M. De Francesco wrote: > On Monday, September 20, 2021 3:10:36 PM CEST Dan Carpenter wrote: > > On Mon, Sep 20, 2021 at 03:03:44PM +0200, Fabio M. De Francesco wrote: > > > On Monday, September 20, 2021 1:56:47 PM CEST Dan Carpenter wrote: > > > > On Mon, Sep 20, 2021 at 01:53:52AM +0200, Fabio M. De Francesco wrote: > > > > > Change the type of "data" from __le32 to __le16. > > > > > > > > > > > > > You should note in the commit message that: > > > > > > > > The last two bytes of "data" are not initialized so the > le32_to_cpu(data) > > > > technically reads uninitialized data. This can likely be detected by > > > > the KASan checker as reading uninitialized data. But because the bytes > > > > are discarded in the end so this will not affect runtime. > > > > > > > > regards, > > > > dan carpenter > > > > > > > > > > Dear Dan, > > > > > > Thanks for your suggestion about this specific topic. > > > > > > We thought that, since "data" is in bitwise AND with 0xffff before being > > > passed to the callee, it was enough to have reviewers know why we're > doing > > > that change of type with no further explanations. Actually it seems to be > not > > > enough to motivate that change. > > > > > > We will surely use the note you provided. > > > > > > However, since I'm not used to blindly follow suggestions (even if I > trust > > > your words with no doubts at all) without complete understanding of what > I'm > > > doing, I will need to understand what KASan is before copy-paste your > note. > > > > Google is your friend! > > Yes, it is :) > > I think you were referring to the KernelMemorySanitizer (KMSan), a detector > of uses of uninitialized memory (but it seems to not be upstream): > https://github.com/google/kmsan > > Instead you wrote about the The Kernel Address Sanitizer (KASan) that seems > to be a dynamic memory error detector designed to find out-of-bound and use- > after-free bugs (this is upstream): > https://www.kernel.org/doc/html/v5.0/dev-tools/kasan.html > > Can you please confirm? That sounds probably right. > > Back to the code... uninitialised data is not a problem in the old code, it's > just bad design. The new code cannot affect runtime, it's just better design. It would be a problem for KMSan and the kbuild-bot will email you about it. From your commit message "Change the type of "data" from __le32 to __le16." it's not clear you understand why the kbuild-bot will email you and why it's correct to do so. regards, dan carpenter
