• Mark Rutland's avatar
    arm64: avoid returning from bad_mode · 7d9e8f71
    Mark Rutland authored
    Generally, taking an unexpected exception should be a fatal event, and
    bad_mode is intended to cater for this. However, it should be possible
    to contain unexpected synchronous exceptions from EL0 without bringing
    the kernel down, by sending a SIGILL to the task.
    
    We tried to apply this approach in commit 9955ac47
    
     ("arm64:
    don't kill the kernel on a bad esr from el0"), by sending a signal for
    any bad_mode call resulting from an EL0 exception.
    
    However, this also applies to other unexpected exceptions, such as
    SError and FIQ. The entry paths for these exceptions branch to bad_mode
    without configuring the link register, and have no kernel_exit. Thus, if
    we take one of these exceptions from EL0, bad_mode will eventually
    return to the original user link register value.
    
    This patch fixes this by introducing a new bad_el0_sync handler to cater
    for the recoverable case, and restoring bad_mode to its original state,
    whereby it calls panic() and never returns. The recoverable case
    branches to bad_el0_sync with a bl, and returns to userspace via the
    usual ret_to_user mechanism.
    Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
    Fixes: 9955ac47
    
     ("arm64: don't kill the kernel on a bad esr from el0")
    Reported-by: default avatarMark Salter <msalter@redhat.com>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    7d9e8f71
traps.c 17.6 KB