On 11/09/2017 05:04 PM, Andy Lutomirski wrote: > On Thu, Nov 9, 2017 at 4:57 PM, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote: >> On 11/09/2017 04:53 PM, Andy Lutomirski wrote: >>>> The KAISER code attempts to "poison" the user portion of the kernel page >>>> tables. It detects the entries pages that it wants that it wants to >>>> poison in two ways: >>>> * Looking for addresses >= PAGE_OFFSET >>>> * Looking for entries without _PAGE_USER set >>> What do you mean "poison"? >> >> I meant the _PAGE_NX magic that we do in here: >> >> https://git.kernel.org/pub/scm/linux/kernel/git/daveh/x86-kaiser.git/commit/?h=kaiser-414rc7-20171108&id=c4f7d0819170761f092fcf2327b85b082368e73a >> >> to ensure that userspace is unable to run on the kernel PGD. > > Aha, I get it. Why not just drop the _PAGE_USER check? You could > instead warn if you see a _PAGE_USER page that doesn't have the > correct address for the vsyscall. The _PAGE_USER check helps us with kernel things that want to create mappings below PAGE_OFFSET. The EFI code was the prime user for this. Without this, we poison the EFI mappings and the EFI calls die. I think there might have also been a case for the secondary CPU bringup that needed hacking if we didn't do this. -- 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>
