On Tue, Jun 19, 2018 at 05:51:46PM +0200, Ard Biesheuvel wrote: > On 19 June 2018 at 17:50, Will Deacon <[email protected]> wrote: > > On Tue, Jun 19, 2018 at 05:40:26PM +0200, Ard Biesheuvel wrote: > >> On 19 June 2018 at 17:37, Will Deacon <[email protected]> wrote: > >> > On Tue, Jun 19, 2018 at 05:29:03PM +0200, Ard Biesheuvel wrote: > >> >> On 19 June 2018 at 17:28, Will Deacon <[email protected]> wrote: > >> >> > On Tue, Jun 19, 2018 at 05:23:41PM +0200, Ard Biesheuvel wrote: > >> >> >> On 19 June 2018 at 17:20, Will Deacon <[email protected]> wrote: > >> >> >> > On Wed, May 30, 2018 at 11:53:20AM +0200, Ard Biesheuvel wrote: > >> >> >> >> On 30 May 2018 at 11:14, Will Deacon <[email protected]> wrote: > >> >> >> >> > On Wed, May 30, 2018 at 12:48:06PM +0800, YaoJun wrote: > >> >> >> >> >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > >> >> >> >> >> index 2dbb2c9f1ec1..ac4b22c7e435 100644 > >> >> >> >> >> --- a/arch/arm64/mm/mmu.c > >> >> >> >> >> +++ b/arch/arm64/mm/mmu.c > >> >> >> >> >> @@ -551,6 +551,10 @@ static int __init > >> >> >> >> >> map_entry_trampoline(void) > >> >> >> >> >> __create_pgd_mapping(tramp_pg_dir, pa_start, > >> >> >> >> >> TRAMP_VALIAS, PAGE_SIZE, > >> >> >> >> >> prot, pgd_pgtable_alloc, 0); > >> >> >> >> >> > >> >> >> >> >> + update_mapping_prot(__pa_symbol(tramp_pg_dir), > >> >> >> >> >> + (unsigned long)tramp_pg_dir, > >> >> >> >> >> + PGD_SIZE, PAGE_KERNEL_RO); > >> >> >> >> > > >> >> >> >> > Hmm, I like the idea but is there a risk that the page table > >> >> >> >> > has been mapped > >> >> >> >> > as part of a block entry, which we can't safely split at this > >> >> >> >> > point (i.e. > >> >> >> >> > we'll run into one of the BUG_ONs in the mapping code)? > >> >> >> >> > > >> >> >> >> > >> >> >> >> We'd need to create a separate segment for it initially so the > >> >> >> >> mapping > >> >> >> >> is already at the right granularity. > >> >> >> > > >> >> >> > Why do you think that's the case? I can't see anything that > >> >> >> > guarantees this > >> >> >> > for the page table itself. > >> >> >> > > >> >> >> > >> >> >> We'd need to pass NO_BLOCK_MAPPINGS to map_kernel_segment(), > >> >> >> obviously, but that shouldn't hurt since that segment is relatively > >> >> >> tiny anyway. > >> >> > > >> >> > Ah right, with NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS, I agree that > >> >> > we're good. > >> >> > Ideally, we'd move {idmap,swapper,tramp}_pg_dir into .rodata... > >> >> > > >> >> > >> >> idmap and tramp yes, but swapper needs to be modifiable at runtime, no? > >> > > >> > Right, but couldn't we swizzle the permissions in e.g. set_pmd? We could > >> > even predicate that on a sanity check of the prot. > >> > > >> > >> Swizzle the permissions of the entire .rodata segment? That sounds > >> doable, but there is a whole class of data that belongs in this > >> category, and I think PaX/grsecurity had an API for that (but I don't > >> think anyone is upstreaming that yet). So let's not reinvent that > >> wheel for swapper_pg_dir only. > > > > I wasn't thinking of the whole .rodata segment -- just the page containing > > the entry being modified, but ok. > > That means we will need to map .rodata down to pages as well, or at > least avoid contiguous mappings.
Doesn't it already avoid those? Will
