On Thu, 3 Dec 2015, Dave Hansen wrote: > Today, for normal faults and page table walks, we check the VMA > and/or PTE to ensure that it is compatible with the action. For > instance, if we get a write fault on a non-writeable VMA, we > SIGSEGV. > > We try to do the same thing for protection keys. Basically, we > try to make sure that if a user does this: > > mprotect(ptr, size, PROT_NONE); > *ptr = foo; > > they see the same effects with protection keys when they do this: > > mprotect(ptr, size, PROT_READ|PROT_WRITE); > set_pkey(ptr, size, 4); > wrpkru(0xffffff3f); // access disable pkey 4 > *ptr = foo; > > The state to do that checking is in the VMA, but we also > sometimes have to do it on the page tables only, like when doing > a get_user_pages_fast() where we have no VMA. > > We add two functions and expose them to generic code: > > arch_pte_access_permitted(pte_flags, write) > arch_vma_access_permitted(vma, write) > > These are, of course, backed up in x86 arch code with checks > against the PTE or VMA's protection key. > > But, there are also cases where we do not want to respect > protection keys. When we ptrace(), for instance, we do not want > to apply the tracer's PKRU permissions to the PTEs from the > process being traced. > > Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>