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

Message

Alexandre Ghiti Oct. 6, 2023, 9:29 a.m. UTC

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.

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 | 263 ++++++++++++++++++++++++++++++++-------
 2 files changed, 227 insertions(+), 48 deletions(-)