Re: [PATCH 1/2] powerpc/vdso: Fix VDSO data access when running in a non-root time namespace

[Christophe Leroy]

Le 06/09/2024 à 14:23, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> > When running in a non-root time namespace, the global VDSO data page
> > is replaced by a dedicated namespace data page and the global data
> > page is mapped next to it. Detailed explanations can be found at
> > commit 660fd04f9317 ("lib/vdso: Prepare for time namespace support").
> >
> > When it happens, __kernel_get_syscall_map and __kernel_get_tbfreq
> > and __kernel_sync_dicache don't work anymore because they read 0
> > instead of the data they need.
> >
> > To address that, clock_mode has to be read. When it is set to
> > VDSO_CLOCKMODE_TIMENS, it means it is a dedicated namespace data page
> > and the global data is located on the following page.
> >
> > Add a macro called get_realdatapage which reads clock_mode and add
> > PAGE_SIZE to the pointer provided by get_datapage macro when
> > clock_mode is equal to VDSO_CLOCKMODE_TIMENS. Use this new macro
> > instead of get_datapage macro except for time functions as they handle
> > it internally.
> >
> > Fixes: 74205b3fc2ef ("powerpc/vdso: Add support for time namespaces")
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
>   
> Oops.
>
> I guess it should also have:
>
>    Cc: stable@xxxxxxxxxxxxxxx # v5.13+
>    Reported-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
>    Closes: https://lore.kernel.org/all/ZtnYqZI-nrsNslwy@xxxxxxxxx/

Jason only reported a problem with getrandom, the other three are 
"cherry on the cake".

The bug has been there for 3 years, I'm sure it can stay 3-4 more weeks, 
I'm not sure there is a need to apply it in both trees.

As far as I understood Jason was about to squash the fix into his tree 
so I was expecting him to apply patch 1 before "vDSO getrandom 
implementation for powerpc" patches and then squash patch 2 in place.

> Jason how do you want to handle this?
>
> I can put patch 1 in a topic branch that we both merge? Then you can
> apply patch 2 on top of that merge in your tree.
>
> Or we could both apply patch 1 to our trees, it might lead to a conflict
> but it wouldn't be anything drastic.