Re: [PATCH v2 0/2] riscv: Fix set_memory_XX() and set_direct_map_XX()

Re: [PATCH v2 0/2] riscv: Fix set_memory_XX() and set_direct_map_XX()

[Alexandre Ghiti]

On 27/10/2023 16:32, Alexandre Ghiti wrote:
> Those 2 patches fix the set_memory_XX() and set_direct_map_XX() APIs, which
> in turn fix STRICT_KERNEL_RWX and memfd_secret(). Those were broken since the
> permission changes were not applied to the linear mapping because the linear
> mapping is mapped using hugepages and walk_page_range_novma() does not split
> such mappings.
>
> To fix that, patch 1 disables PGD mappings in the linear mapping as it is
> hard to propagate changes at this level in *all* the page tables, this has the
> downside of disabling PMD mapping for sv32 and PUD (1GB) mapping for sv39 in
> the linear mapping (for specific kernels, we could add a Kconfig to enable
> ARCH_HAS_SET_DIRECT_MAP and STRICT_KERNEL_RWX if needed, I'm pretty sure we'll
> discuss that).
>
> patch 2 implements the split of the huge linear mappings so that
> walk_page_range_novma() can properly apply the permissions. The whole split is
> protected with mmap_sem in write mode, but I'm wondering if that's enough,
> any opinion on that is appreciated.
>
> Changes in v2:
> - Fix rv32 build
> - Rebase on top of 6.6-rc6
> - Move the flush_tlb_all outside the mmap_lock
>
> Alexandre Ghiti (2):
>    riscv: Don't use PGD entries for the linear mapping
>    riscv: Fix set_memory_XX() and set_direct_map_XX() by splitting huge
>      linear mappings
>
>   arch/riscv/mm/init.c     |  12 +-
>   arch/riscv/mm/pageattr.c | 270 +++++++++++++++++++++++++++++++++------
>   2 files changed, 236 insertions(+), 46 deletions(-)
>

Any feedback from anyone? That's a fix I'd like to see merged in 6.7, if 
no objection, I'll ask for Palmer to take it.

Thanks,

Alex