Messages in this thread | | | From | "Chang S. Bae" <> | Subject | [PATCH 00/15] x86: Enable FSGSBASE instructions | Date | Mon, 19 Mar 2018 10:49:12 -0700 |
| |
FSGSBASE is 64-bit instruction set to allow read/write FS/GS base from any privilege. As introduced from Ivybridge, enabling effort has been revolving quite long [2,3,4] for various reasons. After extended discussions [1], this patchset is proposed to introduce new ABIs of customizing FS/GS base (separate from its selector).
FSGSBASE-enabled VM can be located on hosts with either HW virtualization or SW emulation. KVM advertises FSGSBASE when physical CPU has and emulation is supported in QEMU/TCG [5]. In a pool of mixed systems, VMM may disable FSGSBASE for seamless VM migrations [6].
A couple of major benefits are expected. Kernel will have performance improvement in context switch by skipping MSR write for GS base. User-level programs (such as JAVA-based) benefit from avoiding system calls to edit FS/GS base.
Changes when FSGSBASE enabled: * In context switch, a thread's FS/GS base is secured regardless of its selector [1]. * (Subsequently) when ptracer updates FS/GS base, it is (always) carried onto the tracee. This is an outcome of discussions with our GDB contact. Also, checked with other toolchains [7, 8]. * On paranoid entry, GS base is compared with the kernel’s to decide the necessity of SWAPGS.
[1] Recent discussion on LKML: https://marc.info/?t=150147053700001&r=1&w=2 [2] Andy Lutomirski’s rebase work : https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/log/?h=x86/fsgsbase [3] Patch set shown in year 2016: https://marc.info/?t=145857711900001&r=1&w=2 [4] First patch set: https://lkml.org/lkml/2015/4/10/573 [5] QEMU with FSGSBASE emulation: https://github.com/qemu/qemu/blob/026aaf47c02b79036feb830206cfebb2a726510d/target/i386/translate.c#L8186 [6] 5-level EPT: http://lkml.kernel.org/r/9ddf602b-6c8b-8c1e-ab46-07ed12366593@redhat.com [7] RR/FSGSBASE: https://mail.mozilla.org/pipermail/rr-dev/2018-March/000616.html [8] CRIU/FSGSBASE: https://lists.openvz.org/pipermail/criu/2018-March/040654.html
Andi Kleen (1): x86/fsgsbase/64: Add intrinsics/macros for FSGSBASE instructions
Andy Lutomirski (4): x86/fsgsbase/64: Make ptrace read FS/GS base accurately x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE x86/fsgsbase/64: Preserve FS/GS state in __switch_to if FSGSBASE is on x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit
Chang S. Bae (10): x86/fsgsbase/64: Introduce FS/GS base helper functions x86/fsgsbase/64: Use FS/GS base helpers in core dump x86/fsgsbase/64: Factor out load FS/GS segments from __switch_to x86/ptrace: A new macro to get an offset of user_regs_struct x86/fsgsbase/64: Add putregs() to handle multiple elements' setting x86/fsgsbase/64: putregs() in a reverse order x86/fsgsbase/64: Enable FSGSBASE instructions in helper functions x86/fsgsbase/64: When copying a thread, use FSGSBASE if enabled x86/fsgsbase/64: With FSGSBASE, compare GS bases on paranoid_entry x86/fsgsbase/64: Support legacy behavior when FS/GS updated by ptracer
Documentation/admin-guide/kernel-parameters.txt | 2 + arch/x86/entry/entry_64.S | 54 ++++- arch/x86/include/asm/elf.h | 6 +- arch/x86/include/asm/fsgsbase.h | 200 +++++++++++++++++ arch/x86/include/asm/inst.h | 15 ++ arch/x86/kernel/cpu/common.c | 20 ++ arch/x86/kernel/process_64.c | 274 ++++++++++++++++++++---- arch/x86/kernel/ptrace.c | 253 ++++++++++++++++------ 8 files changed, 696 insertions(+), 128 deletions(-) create mode 100644 arch/x86/include/asm/fsgsbase.h
-- 2.7.4
| |