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

[Michael Ellerman]

Christophe Leroy <christophe.leroy at csgroup.eu> 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 at csgroup.eu>
 
Oops.

I guess it should also have:

  Cc: stable at vger.kernel.org # v5.13+
  Reported-by: Jason A. Donenfeld <Jason at zx2c4.com>
  Closes: https://lore.kernel.org/all/ZtnYqZI-nrsNslwy@zx2c4.com/

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.

cheers