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    Subject[tip:x86/urgent] x86/umip: Identify the STR and SLDT instructions
    Commit-ID:  6e2a3064d6a86094fecc20cd430fd96aaa801687
    Gitweb: https://git.kernel.org/tip/6e2a3064d6a86094fecc20cd430fd96aaa801687
    Author: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
    AuthorDate: Mon, 13 Nov 2017 22:29:44 -0800
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Tue, 14 Nov 2017 08:38:09 +0100

    x86/umip: Identify the STR and SLDT instructions

    The STR and SLDT instructions are not emulated by the UMIP code, thus
    there's no functionality in the decoder to identify them.

    However, a subsequent commit will introduce a warning about the use
    of all the instructions that UMIP protect/changes, not only those that
    are emulated.

    A first step for that is to add the ability to decode/identify them.

    Plus, now that STR and SLDT are identified, we need to explicitly avoid
    their emulation (i.e., not rely on successful identification). Group
    together all the cases that we do not want to emulate: STR, SLDT and user
    long mode processes.

    Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Paolo Bonzini <pbonzini@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Tony Luck <tony.luck@intel.com>
    Cc: ricardo.neri@intel.com
    Link: http://lkml.kernel.org/r/1510640985-18412-4-git-send-email-ricardo.neri-calderon@linux.intel.com
    [ Rewrote the changelog, fixed ugly col80 artifact. ]
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    arch/x86/kernel/umip.c | 24 ++++++++++++++++--------
    1 file changed, 16 insertions(+), 8 deletions(-)

    diff --git a/arch/x86/kernel/umip.c b/arch/x86/kernel/umip.c
    index 6ba82be..1f1f2d5 100644
    --- a/arch/x86/kernel/umip.c
    +++ b/arch/x86/kernel/umip.c
    @@ -78,7 +78,9 @@

    #define UMIP_INST_SGDT 0 /* 0F 01 /0 */
    #define UMIP_INST_SIDT 1 /* 0F 01 /1 */
    -#define UMIP_INST_SMSW 3 /* 0F 01 /4 */
    +#define UMIP_INST_SMSW 2 /* 0F 01 /4 */
    +#define UMIP_INST_SLDT 3 /* 0F 00 /0 */
    +#define UMIP_INST_STR 4 /* 0F 00 /1 */

    /**
    * identify_insn() - Identify a UMIP-protected instruction
    @@ -118,10 +120,16 @@ static int identify_insn(struct insn *insn)
    default:
    return -EINVAL;
    }
    + } else if (insn->opcode.bytes[1] == 0x0) {
    + if (X86_MODRM_REG(insn->modrm.value) == 0)
    + return UMIP_INST_SLDT;
    + else if (X86_MODRM_REG(insn->modrm.value) == 1)
    + return UMIP_INST_STR;
    + else
    + return -EINVAL;
    + } else {
    + return -EINVAL;
    }
    -
    - /* SLDT AND STR are not emulated */
    - return -EINVAL;
    }

    /**
    @@ -267,10 +275,6 @@ bool fixup_umip_exception(struct pt_regs *regs)
    if (!regs)
    return false;

    - /* Do not emulate 64-bit processes. */
    - if (user_64bit_mode(regs))
    - return false;
    -
    /*
    * If not in user-space long mode, a custom code segment could be in
    * use. This is true in protected mode (if the process defined a local
    @@ -322,6 +326,10 @@ bool fixup_umip_exception(struct pt_regs *regs)
    if (umip_inst < 0)
    return false;

    + /* Do not emulate SLDT, STR or user long mode processes. */
    + if (umip_inst == UMIP_INST_STR || umip_inst == UMIP_INST_SLDT || user_64bit_mode(regs))
    + return false;
    +
    if (emulate_umip_insn(&insn, umip_inst, dummy_data, &dummy_data_size))
    return false;

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