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SubjectRe: [PATCH v5 0/4] x86: modify_ldt improvement, test, and config option
On 07/28/2015 01:29 AM, Andy Lutomirski wrote:
> This is intended for x86/urgent. Sorry for taking so long, but it
> seemed nice to avoid breaking Xen.
>
> This fixes the "dazed and confused" issue which was exposed by the
> CVE-2015-5157 fix. It's also probably a good general attack surface
> reduction, and it replaces some scary code with IMO less scary code.
>
> Also, servers and embedded systems should probably turn off modify_ldt.
> This makes that possible.
>
> Boris, could I get a Tested-by, assuming this works for you?

As far as Xen guests are concerned,

Tested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

But ldt_gdt_32 test segfaults on 64-bit kernels. Baremetal and virt. I
thought it worked for me before but can't reproduce this with older
patches. Does it work for you?


-boris


>
> Willy and Kees: I left the config option alone. The -tiny people will
> like it, and we can always add a sysctl of some sort later.
>
> Changes from v4:
> - Fix Xen even better (patch 1 is new).
> - Reorder the patches to make a little more sense.
>
> Changes from v3:
> - Hopefully fixed Xen.
> - Fixed 32-bit test case on 32-bit native kernel.
> - Fix bogus vumnap for some LDT sizes.
> - Strengthen test case to check all LDT sizes (catches bogus vunmap).
> - Lots of cleanups, mostly from Borislav.
> - Simplify IPI code using on_each_cpu_mask.
>
> Changes from v2:
> - Allocate ldt_struct and the LDT entries separately. This should fix Xen.
> - Stop using write_ldt_entry, since I'm pretty sure it's unnecessary now
> that we no longer mutate an in-use LDT. (Xen people, can you check?)
>
> Changes from v1:
> - The config option is new.
> - The test case is new.
> - Fixed a missing allocation failure check.
> - Fixed a use-after-free on fork().
>
> Andy Lutomirski (4):
> x86/xen: Unmap aliases in xen_alloc_ldt and xen_free_ldt
> x86/ldt: Make modify_ldt synchronous
> selftests/x86, x86/ldt: Add a selftest for modify_ldt
> x86/ldt: Make modify_ldt optional
>
> arch/x86/Kconfig | 17 ++
> arch/x86/include/asm/desc.h | 15 -
> arch/x86/include/asm/mmu.h | 5 +-
> arch/x86/include/asm/mmu_context.h | 68 ++++-
> arch/x86/kernel/Makefile | 3 +-
> arch/x86/kernel/cpu/common.c | 4 +-
> arch/x86/kernel/cpu/perf_event.c | 16 +-
> arch/x86/kernel/ldt.c | 262 +++++++++--------
> arch/x86/kernel/process_64.c | 6 +-
> arch/x86/kernel/step.c | 8 +-
> arch/x86/power/cpu.c | 3 +-
> arch/x86/xen/enlighten.c | 12 +
> kernel/sys_ni.c | 1 +
> tools/testing/selftests/x86/Makefile | 2 +-
> tools/testing/selftests/x86/ldt_gdt.c | 520 ++++++++++++++++++++++++++++++++++
> 15 files changed, 787 insertions(+), 155 deletions(-)
> create mode 100644 tools/testing/selftests/x86/ldt_gdt.c
>



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