Re: [PATCH v4 0/7] mm/mprotect: Fix dax puds

[Andrew Morton]

On Wed, 7 Aug 2024 17:34:10 -0400 Peter Xu <peterx@xxxxxxxxxx> wrote:

> The problem is mprotect() will skip the dax 1G PUD while it shouldn't;
> meanwhile it'll dump some bad PUD in dmesg.  Both of them look like (corner
> case) bugs to me.. where:
> 
>   - skipping the 1G pud means mprotect() will succeed even if the pud won't
>     be updated with the correct permission specified. Logically that can
>     cause e.g. in mprotect(RO) then write the page can cause data corrupt,
>     as the pud page will still be writable.
> 
>   - the bad pud will generate a pr_err() into dmesg, with no limit so far I
>     can see.  So I think it means an userspace can DoS the kernel log if it
>     wants.. simply by creating the PUD and keep mprotect-ing it
> 

I edited this important info into the [0/n] text, thanks.

So current kernels can be made to spew into the kernel logs?  That's
considered serious.  Can unprivileged userspace code do this?