• Fredrik Strupe's avatar
    arm64: armv8_deprecated: Fix undef_hook mask for thumb setend · fc226601
    Fredrik Strupe authored
    For thumb instructions, call_undef_hook() in traps.c first reads a u16,
    and if the u16 indicates a T32 instruction (u16 >= 0xe800), a second
    u16 is read, which then makes up the the lower half-word of a T32
    instruction. For T16 instructions, the second u16 is not read,
    which makes the resulting u32 opcode always have the upper half set to
    0.
    
    However, having the upper half of instr_mask in the undef_hook set to 0
    masks out the upper half of all thumb instructions - both T16 and T32.
    This results in trapped T32 instructions with the lower half-word equal
    to the T16 encoding of setend (b650) being matched, even though the upper
    half-word is not 0000 and thus indicates a T32 opcode.
    
    An example of such a T32 instruction is eaa0b650, which should raise a
    SIGILL since T32 instructions with an eaa prefix are unallocated as per
    Arm ARM, but instead works as a SETEND because the second half-word is set
    to b650.
    
    This patch fixes the issue by extending instr_mask to include the
    upper u32 half, which will still match T16 instructions where the upper
    half is 0, but not T32 instructions.
    
    Fixes: 2d888f48 ("arm64: Emulate SETEND for AArch32 tasks")
    Cc: <stable@vger.kernel.org> # 4.0.x-
    Reviewed-by: default avatarSuzuki K Poulose <suzuki.poulose@arm.com>
    Signed-off-by: default avatarFredrik Strupe <fredrik@strupe.net>
    Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
    fc226601
armv8_deprecated.c 15.4 KB