[PATCH 0/2] ARM: prctl: Reject PR_SET_MDWE where not supported

[Zev Weiss]

On Thu, Feb 08, 2024 at 01:20:57AM PST, Russell King (Oracle) wrote:
>Hi,
>
>Where is patch 1 of this series? It doesn't seem to have been Cc'd to
>linux-arm-kernel. Therefore, this can't be reviewed.
>

It went to (among others) the linux-parisc list, but not 
linux-arm-kernel as scripts/get_maintainers.pl didn't list it for that 
patch:
https://lore.kernel.org/lkml/20240208012620.32604-5-zev@bewilderbeest.net/

I think I've gotten differing opinions from different subsystem 
maintainers on this, but FWIW my usual default approach is to use 
scripts/get_maintainer.pl on each patch and then add the set-union of 
them all to the cover letter for context; I'll try to remember the 
preference for linux-arm-kernel though.

Is the link above sufficient for now, or shall I resend the series?


Thanks,
Zev


>Thanks.
>
>On Wed, Feb 07, 2024 at 05:26:18PM -0800, Zev Weiss wrote:
>> Hello,
>>
>> I noticed after a recent kernel update that my ARM926 system started
>> segfaulting on any execve() after calling prctl(PR_SET_MDWE).  After
>> some investigation it appears that ARMv5 is incapable of providing the
>> appropriate protections for MDWE, since any readable memory is also
>> implicitly executable.
>>
>> (Note that I'm not an expert in either ARM arch details or the mm
>> subsystem, so please bear with me if I've botched something in the
>> above analysis.)
>>
>> The prctl_set_mdwe() function already had some special-case logic
>> added disabling it on PARISC (commit 793838138c15, "prctl: Disable
>> prctl(PR_SET_MDWE) on parisc"); this patch series (1) generalizes that
>> check to use an arch_*() function, and (2) adds a corresponding
>> override for ARM to disable MDWE on pre-ARMv6 CPUs.
>>
>> With the series applied, prctl(PR_SET_MDWE) is rejected on ARMv5 and
>> subsequent execve() calls (as well as mmap(PROT_READ|PROT_WRITE)) can
>> succeed instead of unconditionally failing; on ARMv6 the prctl works
>> as it did previously.
>>
>> Since this was effectively a userspace-breaking change in v6.3 (with
>> newer MDWE-aware userspace on older pre-MDWE kernels the prctl would
>> simply fail safely) I've CCed -stable for v6.3+, though since the
>> patches depend on the PARISC one above it will only apply cleanly on
>> the linux-6.6.y and linux-6.7.y branches, since at least at time of
>> writing the 6.3 through 6.5 branches don't have that patch backported
>> (due to further missing dependencies [0]).
>>
>>
>> Thanks,
>> Zev
>>
>> [0] https://lore.kernel.org/all/2023112456-linked-nape-bf19@gregkh/
>>
>> Zev Weiss (2):
>>   prctl: Generalize PR_SET_MDWE support check to be per-arch
>>   ARM: prctl: Reject PR_SET_MDWE on pre-ARMv6
>>
>>  arch/arm/include/asm/mman.h    | 14 ++++++++++++++
>>  arch/parisc/include/asm/mman.h | 14 ++++++++++++++
>>  include/linux/mman.h           |  8 ++++++++
>>  kernel/sys.c                   |  7 +++++--
>>  4 files changed, 41 insertions(+), 2 deletions(-)
>>  create mode 100644 arch/arm/include/asm/mman.h
>>  create mode 100644 arch/parisc/include/asm/mman.h
>>
>> --
>> 2.43.0
>>
>>
>> _______________________________________________
>> linux-arm-kernel mailing list
>> linux-arm-kernel at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
>
>-- 
>RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
>FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!