On Sun, Dec 10, 2017 at 10:47 PM, Andy Lutomirski <l...@kernel.org> wrote:
> I'm getting reasonably happy with this. It still needs more testing,
> but I want to get it out there.
>
> The main things that need testing are the 5-level case for the both
> vsyscalls and the LDT. I'm getting a double-fault in ldt_gdt_64,
> but I haven't checked whether it's a bug in this series, and it
> kind of looks like it isn't. I'll figure it out in the morning.
> The docs also want updating for the 5 level case.
>
The actual failure looks a lot like the ESPFIX stacks aren't mapped in
the usermode tables, which reinforces my old belief that this bit of
code is bogus:
/*
* Just copy the top-level PGD that is mapping the espfix area to
* ensure it is mapped into the user page tables.
*
* For 5-level paging, the espfix pgd was populated when
* pti_init() pre-populated all the pgd entries. The above
* p4d_alloc() would never do anything and the p4d_populate() would
* be done to a p4d already mapped in the userspace pgd.
*/
#ifdef CONFIG_PAGE_TABLE_ISOLATION
if (CONFIG_PGTABLE_LEVELS <= 4) {
set_pgd(kernel_to_user_pgdp(pgd),
__pgd(_KERNPG_TABLE | (p4d_pfn(*p4d) << PAGE_SHIFT)));
}
#endif
Of course, the comment is even more wrong with this series applied,
but I think it's been wrong all along.
I'll fix it in the morning if no one beats me to it.
(Hint: this can be tested in QEMU with -machine accel=tcg -cpu qemu64,+la57)
> Changes from v1:
> - vsyscalls actually work.
> - Added the "Warn and fail" patch to prevent the testing goof I had on v1.
> - Lots of cleanups
>
> Andy Lutomirski (6):
> x86/pti: Vastly simplify pgd synchronization
> Revert "x86/mm/pti: Disable native VSYSCALL"
> x86/vsyscall/64: Explicitly set _PAGE_USER in the pagetable hierarchy
> x86/vsyscall/64: Warn and fail vsyscall emulation in NATIVE mode
> x86/pti: Map the vsyscall page if needed
> x86/pti: Put the LDT in its own PGD if PTI is on
>
> Documentation/x86/x86_64/mm.txt | 11 ++-
> arch/x86/Kconfig | 8 --
> arch/x86/entry/vsyscall/vsyscall_64.c | 37 ++++++++-
> arch/x86/include/asm/mmu_context.h | 33 +++++++-
> arch/x86/include/asm/pgtable.h | 6 +-
> arch/x86/include/asm/pgtable_64.h | 77 ++++++++----------
> arch/x86/include/asm/pgtable_64_types.h | 2 +
> arch/x86/include/asm/processor.h | 23 ++++--
> arch/x86/include/asm/vsyscall.h | 1 +
> arch/x86/kernel/ldt.c | 138
> +++++++++++++++++++++++++++++---
> arch/x86/mm/pti.c | 115 ++++++++++++++++----------
> 11 files changed, 331 insertions(+), 120 deletions(-)
>
> --
> 2.13.6
>
