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Message-ID: <ZtsKW3LLfwmz7icC@zx2c4.com> Date: Fri, 6 Sep 2024 15:57:47 +0200 From: "Jason A. Donenfeld" <Jason@...c4.com> To: Michael Ellerman <mpe@...erman.id.au> 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 On Fri, Sep 06, 2024 at 03:43:17PM +0200, Jason A. Donenfeld wrote: > On Fri, Sep 06, 2024 at 10:23:08PM +1000, Michael Ellerman wrote: > > 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. > > The merge window for 6.12 is pretty soon. Why don't I just take this in > my random.git tree (with your ack) as a prereq to the ppc vDSO work. > It'll slide in _before_ Christophe's other commits, and then the > separate vgetrandom fixup will be squashed in the right place there. > > And then it'll hit stable when that's submitted for 6.12. It's an old > bug that nobody noticed, and time namespaces are kind of obscure, so I > think waiting a week and a half for the merge window to open is probably > fine. So I've just done this (preliminarily, pending Michael's approval), and it comes out decently clean and everything works fine. The commit sequence becomes: ... c206cd11e7f2 selftests: vDSO: ensure vgetrandom works in a time namespace ... e59cc170924c powerpc/vdso: Fix VDSO data access when running in a non-root time namespace 887e7a77dc99 mm: Define VM_DROPPABLE for powerpc/32 f2ee39ec52c2 powerpc/vdso32: Add crtsavres 994148e87080 powerpc/vdso: Refactor CFLAGS for CVDSO build c49ec121a6dd powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO32 <-- fixed up a8a5e16cde32 powerpc/vdso: Wire up getrandom() vDSO implementation on VDSO64 So I'm happy with this. Jason
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