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    SubjectRe: [PATCH 0/7] Enable LASS (Linear Address space Separation)
    From
    Yian,

    I added a few missing lists pertaining to KVM, MM and documentation
    since these patches impact them.

    In future, scripts/get_maintainer.pl can help you with generating the
    relevant maintainers and lists.

    On 1/9/2023 9:51 PM, Yian Chen wrote:
    > LASS (Linear Address Space Separation) is a security
    > extension that prevents speculative address accesses across
    > user/kernel mode. The LASS details have been published in
    > Chapter 11 in
    > https://cdrdv2.intel.com/v1/dl/getContent/671368
    >
    > LASS works in 64-bit mode only and partitions the 64-bit
    > virtual address space into two halves:
    > 1. Lower half (LA[63]=0) --> user space
    > 2. Upper half (LA[63]=1) --> kernel space
    > When LASS is enabled, a general protection #GP(0) fault will
    > be generated if software accesses the address from the half in
    > which it resides to another half, e.g., either from user space
    > to upper half, or from kernel space to lower half. This
    > protection applies to data access, code execution, cache line
    > flushing instructions.
    >
    > Almost all kernel accesses are to the upper half of the virtual
    > address space. However, there are valid reasons for kernel to
    > access the lower half. For these cases, kernel can temporarily
    > suspend the enforcement of LASS by disabling SMAP (Supervisor
    > Mode Access Prevention).
    >
    > Kernel access to copy data to/from user addresses already
    > disables SMAP using the stac()/clac() functions. New functions
    > low_addr_access_begin()/low_addr_access_end() are added to
    > also disable/enable SMAP around other code that legitimately
    > needs to access the lower half of the virtual address space.
    >
    > User space cannot use any kernel address while LASS is
    > enabled. Less fortunately, legacy vsyscall functions used
    > by old version of glibc are located in the address range
    > 0xffffffffff600000-0xffffffffff601000 and emulated in kernel.
    > Therefore, to comply with LASS policy, the legacy vsyscall is
    > disabled by default. I am looking for input from Andy and
    > others if this approach is acceptable.
    >
    > This patch set by default enforces LASS when the platform
    > supports it. It can be disabled via the command line parameter
    > "clearcpuid" or by setting "vsyscall=emulate/xonly".
    >
    > As of now there is no publicly available CPU supporting LASS.
    > The first one to support LASS is Sierra Forest line. The Intel
    > Simics® Simulator was used as software development and testing
    > vehicle for this patch set.
    >
    > Paul Lai (1):
    > x86/kvm: Expose LASS feature to VM guest
    >
    > Yian Chen (6):
    > x86/cpu: Enumerate LASS CPUID and CR4 bits
    > x86: Add CONFIG option X86_LASS
    > x86/cpu: Disable kernel LASS when patching kernel alternatives
    > x86/vsyscall: Setup vsyscall to compromise LASS protection
    > x86/cpu: Enable LASS (Linear Address Space Separation)
    > x86/cpu: Set LASS as pinning sensitive CR4 bit
    >

    It's usually good practice to include a base-commit to make it easier to
    apply these patches.

    > .../admin-guide/kernel-parameters.txt | 12 +++++++----
    > arch/x86/Kconfig | 10 +++++++++
    > arch/x86/entry/vsyscall/vsyscall_64.c | 14 +++++++++++++
    > arch/x86/include/asm/cpufeatures.h | 1 +
    > arch/x86/include/asm/disabled-features.h | 8 ++++++-
    > arch/x86/include/asm/kvm_host.h | 3 ++-
    > arch/x86/include/asm/smap.h | 13 ++++++++++++
    > arch/x86/include/uapi/asm/processor-flags.h | 2 ++
    > arch/x86/kernel/Makefile | 2 ++
    > arch/x86/kernel/alternative.c | 21 +++++++++++++++++--
    > arch/x86/kernel/cpu/common.c | 20 +++++++++++++++++-
    > arch/x86/kvm/cpuid.c | 2 +-
    > tools/arch/x86/include/asm/cpufeatures.h | 1 +
    > .../arch/x86/include/asm/disabled-features.h | 8 ++++++-
    > tools/objtool/arch/x86/special.c | 2 ++
    > 15 files changed, 108 insertions(+), 11 deletions(-)
    >

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