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    Subject[PATCH 24/25] objtool: uaccess PUSHF/POPF support
    Add PUSHF / POPF state.uaccess restore logic. This makes
    user_access_save() / user_access_restore() 'work' with objtool.

    XXX: should be merged with the previous patch such that KASAN
    doesn't explode in between. Split for review.

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    ---
    tools/objtool/arch.h | 2 ++
    tools/objtool/arch/x86/decode.c | 4 ++--
    tools/objtool/check.c | 30 ++++++++++++++++++++++++++----
    tools/objtool/check.h | 1 +
    4 files changed, 31 insertions(+), 6 deletions(-)

    --- a/tools/objtool/arch.h
    +++ b/tools/objtool/arch.h
    @@ -43,6 +43,7 @@ enum op_dest_type {
    OP_DEST_REG_INDIRECT,
    OP_DEST_MEM,
    OP_DEST_PUSH,
    + OP_DEST_PUSHF,
    OP_DEST_LEAVE,
    };

    @@ -57,6 +58,7 @@ enum op_src_type {
    OP_SRC_REG_INDIRECT,
    OP_SRC_CONST,
    OP_SRC_POP,
    + OP_SRC_POPF,
    OP_SRC_ADD,
    OP_SRC_AND,
    };
    --- a/tools/objtool/arch/x86/decode.c
    +++ b/tools/objtool/arch/x86/decode.c
    @@ -357,13 +357,13 @@ int arch_decode_instruction(struct elf *
    /* pushf */
    *type = INSN_STACK;
    op->src.type = OP_SRC_CONST;
    - op->dest.type = OP_DEST_PUSH;
    + op->dest.type = OP_DEST_PUSHF;
    break;

    case 0x9d:
    /* popf */
    *type = INSN_STACK;
    - op->src.type = OP_SRC_POP;
    + op->src.type = OP_SRC_POPF;
    op->dest.type = OP_DEST_MEM;
    break;

    --- a/tools/objtool/check.c
    +++ b/tools/objtool/check.c
    @@ -1392,11 +1392,11 @@ static int update_insn_state_regs(struct
    return 0;

    /* push */
    - if (op->dest.type == OP_DEST_PUSH)
    + if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
    cfa->offset += 8;

    /* pop */
    - if (op->src.type == OP_SRC_POP)
    + if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
    cfa->offset -= 8;

    /* add immediate to sp */
    @@ -1653,6 +1653,7 @@ static int update_insn_state(struct inst
    break;

    case OP_SRC_POP:
    + case OP_SRC_POPF:
    if (!state->drap && op->dest.type == OP_DEST_REG &&
    op->dest.reg == cfa->base) {

    @@ -1717,6 +1718,7 @@ static int update_insn_state(struct inst
    break;

    case OP_DEST_PUSH:
    + case OP_DEST_PUSHF:
    state->stack_size += 8;
    if (cfa->base == CFI_SP)
    cfa->offset += 8;
    @@ -1807,7 +1809,7 @@ static int update_insn_state(struct inst
    break;

    case OP_DEST_MEM:
    - if (op->src.type != OP_SRC_POP) {
    + if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
    WARN_FUNC("unknown stack-related memory operation",
    insn->sec, insn->offset);
    return -1;
    @@ -2109,6 +2111,26 @@ static int validate_branch(struct objtoo
    if (update_insn_state(insn, &state))
    return 1;

    + if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
    + if (!state.uaccess_stack) {
    + state.uaccess_stack = 1;
    + } else if (state.uaccess_stack >> 31) {
    + WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
    + return 1;
    + }
    + state.uaccess_stack <<= 1;
    + state.uaccess_stack |= state.uaccess;
    + }
    +
    + if (insn->stack_op.src.type == OP_SRC_POPF) {
    + if (state.uaccess_stack) {
    + state.uaccess = state.uaccess_stack & 1;
    + state.uaccess_stack >>= 1;
    + if (state.uaccess_stack == 1)
    + state.uaccess_stack = 0;
    + }
    + }
    +
    break;

    case INSN_STAC:
    @@ -2126,7 +2148,7 @@ static int validate_branch(struct objtoo
    return 1;
    }

    - if (func_uaccess_safe(func)) {
    + if (func_uaccess_safe(func) && !state.uaccess_stack) {
    WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
    return 1;
    }
    --- a/tools/objtool/check.h
    +++ b/tools/objtool/check.h
    @@ -32,6 +32,7 @@ struct insn_state {
    unsigned char type;
    bool bp_scratch;
    bool drap, end, uaccess;
    + unsigned int uaccess_stack;
    int drap_reg, drap_offset;
    struct cfi_reg vals[CFI_NUM_REGS];
    };

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