Re: [PATCH v2] arm[64]/memremap: don't abuse pfn_valid() to ensure presence of linear map

[Catalin Marinas]

On Fri, Apr 29, 2022 at 03:38:59PM +0200, Ard Biesheuvel wrote:
> On Tue, 26 Apr 2022 at 08:01, Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> > From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> >
> > The semantics of pfn_valid() is to check presence of the memory map for a
> > PFN and not whether a PFN is covered by the linear map. The memory map may
> > be present for NOMAP memory regions, but they won't be mapped in the linear
> > mapping.  Accessing such regions via __va() when they are memremap()'ed
> > will cause a crash.
> >
> > On v5.4.y the crash happens on qemu-arm with UEFI [1]:
> >
> > <1>[    0.084476] 8<--- cut here ---
> > <1>[    0.084595] Unable to handle kernel paging request at virtual address dfb76000
> > <1>[    0.084938] pgd = (ptrval)
> > <1>[    0.085038] [dfb76000] *pgd=5f7fe801, *pte=00000000, *ppte=00000000
> >
> > ...
> >
> > <4>[    0.093923] [<c0ed6ce8>] (memcpy) from [<c16a06f8>] (dmi_setup+0x60/0x418)
> > <4>[    0.094204] [<c16a06f8>] (dmi_setup) from [<c16a38d4>] (arm_dmi_init+0x8/0x10)
> > <4>[    0.094408] [<c16a38d4>] (arm_dmi_init) from [<c0302e9c>] (do_one_initcall+0x50/0x228)
> > <4>[    0.094619] [<c0302e9c>] (do_one_initcall) from [<c16011e4>] (kernel_init_freeable+0x15c/0x1f8)
> > <4>[    0.094841] [<c16011e4>] (kernel_init_freeable) from [<c0f028cc>] (kernel_init+0x8/0x10c)
> > <4>[    0.095057] [<c0f028cc>] (kernel_init) from [<c03010e8>] (ret_from_fork+0x14/0x2c)
> >
> > On kernels v5.10.y and newer the same crash won't reproduce on ARM because
> > commit b10d6bca8720 ("arch, drivers: replace for_each_membock() with
> > for_each_mem_range()") changed the way memory regions are registered in the
> > resource tree, but that merely covers up the problem.
> >
> > On ARM64 memory resources registered in yet another way and there the
> > issue of wrong usage of pfn_valid() to ensure availability of the linear
> > map is also covered.
> >
> > Implement arch_memremap_can_ram_remap() on ARM and ARM64 to prevent access
> > to NOMAP regions via the linear mapping in memremap().
> >
> > Link: https://lore.kernel.org/all/Yl65zxGgFzF1Okac@xxxxxxxxxxxxx
> > Reported-by: "kernelci.org bot" <bot@xxxxxxxxxxxx>
> > Tested-by: Mark Brown <broonie@xxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx      # 5.4+
> > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > ---
> > v2: don't remove pfn_valid() from try_ram_remap(), per Ard
> >
> >  arch/arm/include/asm/io.h   | 3 +++
> >  arch/arm/mm/ioremap.c       | 8 ++++++++
> >  arch/arm64/include/asm/io.h | 4 ++++
> >  arch/arm64/mm/ioremap.c     | 8 ++++++++
> >  4 files changed, 23 insertions(+)
> >
> 
> I think this looks reasonable, but you'll need to split it in two if
> it is going through the respective arch trees.

I guess that would be best. Otherwise, if Andrew picks it up:

Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>