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    Subject[PATCH AUTOSEL for 3.18 057/101] arm64: ptrace: Avoid setting compat FP[SC]R to garbage if get_user fails
    Date
    From: Dave Martin <Dave.Martin@arm.com>

    [ Upstream commit 53b1a742ed251780267a57415bc955bd50f40c3d ]

    If get_user() fails when reading the new FPSCR value from userspace
    in compat_vfp_get(), then garbage* will be written to the task's
    FPSR and FPCR registers.

    This patch prevents this by checking the return from get_user()
    first.

    [*] Actually, zero, due to the behaviour of get_user() on error, but
    that's still not what userspace expects.

    Fixes: 478fcb2cdb23 ("arm64: Debugging support")
    Signed-off-by: Dave Martin <Dave.Martin@arm.com>
    Signed-off-by: Will Deacon <will.deacon@arm.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    arch/arm64/kernel/ptrace.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
    index 2e845f5c8ab2..a12eb17e7985 100644
    --- a/arch/arm64/kernel/ptrace.c
    +++ b/arch/arm64/kernel/ptrace.c
    @@ -785,8 +785,10 @@ static int compat_vfp_set(struct task_struct *target,

    if (count && !ret) {
    ret = get_user(fpscr, (compat_ulong_t *)ubuf);
    - uregs->fpsr = fpscr & VFP_FPSCR_STAT_MASK;
    - uregs->fpcr = fpscr & VFP_FPSCR_CTRL_MASK;
    + if (!ret) {
    + uregs->fpsr = fpscr & VFP_FPSCR_STAT_MASK;
    + uregs->fpcr = fpscr & VFP_FPSCR_CTRL_MASK;
    + }
    }

    fpsimd_flush_task_state(target);
    --
    2.15.1
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