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

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Message-ID: <87r09x3r9v.fsf@mail.lhotse>
Date: Fri, 06 Sep 2024 22:23:08 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Christophe Leroy <christophe.leroy@...roup.eu>, "Jason A . Donenfeld"
 <Jason@...c4.com>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, Nicholas
 Piggin <npiggin@...il.com>, Naveen N Rao <naveen@...nel.org>, Vincenzo
 Frascino <vincenzo.frascino@....com>, Andrei Vagin <avagin@...il.com>
Subject: Re: [PATCH 1/2] powerpc/vdso: Fix VDSO data access when running in
 a non-root time namespace

Christophe Leroy <christophe.leroy@...roup.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@...roup.eu>

Oops.

I guess it should also have:

  Cc: stable@...r.kernel.org # v5.13+
  Reported-by: Jason A. Donenfeld <Jason@...c4.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