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    Subject[PATCH v3 49/75] x86/sev-es: Handle instruction fetches from user-space
    Date
    From: Joerg Roedel <jroedel@suse.de>

    When a #VC exception is triggered by user-space the instruction decoder
    needs to read the instruction bytes from user addresses. Enhance
    vc_decode_insn() to safely fetch kernel and user instructions.

    Signed-off-by: Joerg Roedel <jroedel@suse.de>
    ---
    arch/x86/kernel/sev-es.c | 31 ++++++++++++++++++++++---------
    1 file changed, 22 insertions(+), 9 deletions(-)

    diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
    index 85027fb4177e..c2223c2a28c2 100644
    --- a/arch/x86/kernel/sev-es.c
    +++ b/arch/x86/kernel/sev-es.c
    @@ -165,17 +165,30 @@ static enum es_result vc_decode_insn(struct es_em_ctxt *ctxt)
    enum es_result ret;
    int res;

    - res = vc_fetch_insn_kernel(ctxt, buffer);
    - if (unlikely(res == -EFAULT)) {
    - ctxt->fi.vector = X86_TRAP_PF;
    - ctxt->fi.error_code = 0;
    - ctxt->fi.cr2 = ctxt->regs->ip;
    - return ES_EXCEPTION;
    + if (!user_mode(ctxt->regs)) {
    + res = vc_fetch_insn_kernel(ctxt, buffer);
    + if (unlikely(res == -EFAULT)) {
    + ctxt->fi.vector = X86_TRAP_PF;
    + ctxt->fi.error_code = 0;
    + ctxt->fi.cr2 = ctxt->regs->ip;
    + return ES_EXCEPTION;
    + }
    +
    + insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
    + insn_get_length(&ctxt->insn);
    + } else {
    + res = insn_fetch_from_user(ctxt->regs, buffer);
    + if (res == 0) {
    + ctxt->fi.vector = X86_TRAP_PF;
    + ctxt->fi.cr2 = ctxt->regs->ip;
    + ctxt->fi.error_code = X86_PF_INSTR | X86_PF_USER;
    + return ES_EXCEPTION;
    + }
    +
    + if (!insn_decode(ctxt->regs, &ctxt->insn, buffer, res))
    + return ES_DECODE_FAILED;
    }

    - insn_init(&ctxt->insn, buffer, MAX_INSN_SIZE - res, 1);
    - insn_get_length(&ctxt->insn);
    -
    ret = ctxt->insn.immediate.got ? ES_OK : ES_DECODE_FAILED;

    return ret;
    --
    2.17.1
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