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    Subject[PATCH 4.18 073/235] arm64: fix possible spectre-v1 write in ptrace_hbp_set_event()
    Date
    4.18-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mark Rutland <mark.rutland@arm.com>

    [ Upstream commit 14d6e289a89780377f8bb09de8926d3c62d763cd ]

    It's possible for userspace to control idx. Sanitize idx when using it
    as an array index, to inhibit the potential spectre-v1 write gadget.

    Found by smatch.

    Signed-off-by: Mark Rutland <mark.rutland@arm.com>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/arm64/kernel/ptrace.c | 19 +++++++++++--------
    1 file changed, 11 insertions(+), 8 deletions(-)

    --- a/arch/arm64/kernel/ptrace.c
    +++ b/arch/arm64/kernel/ptrace.c
    @@ -277,19 +277,22 @@ static int ptrace_hbp_set_event(unsigned

    switch (note_type) {
    case NT_ARM_HW_BREAK:
    - if (idx < ARM_MAX_BRP) {
    - tsk->thread.debug.hbp_break[idx] = bp;
    - err = 0;
    - }
    + if (idx >= ARM_MAX_BRP)
    + goto out;
    + idx = array_index_nospec(idx, ARM_MAX_BRP);
    + tsk->thread.debug.hbp_break[idx] = bp;
    + err = 0;
    break;
    case NT_ARM_HW_WATCH:
    - if (idx < ARM_MAX_WRP) {
    - tsk->thread.debug.hbp_watch[idx] = bp;
    - err = 0;
    - }
    + if (idx >= ARM_MAX_WRP)
    + goto out;
    + idx = array_index_nospec(idx, ARM_MAX_WRP);
    + tsk->thread.debug.hbp_watch[idx] = bp;
    + err = 0;
    break;
    }

    +out:
    return err;
    }


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