Re: [PATCH for-9.2] target/riscv: Avoid bad shift in riscv_cpu_do_interrupt()

[Alistair Francis]

On Thu, Nov 28, 2024 at 7:39 PM Peter Maydell <peter.maydell@linaro.org> wrote:
>
> In riscv_cpu_do_interrupt() we use the 'cause' value we got out of
> cs->exception as a shift value.  However this value can be larger
> than 31, which means that "1 << cause" is undefined behaviour,
> because we do the shift on an 'int' type.
>
> This causes the undefined behaviour sanitizer to complain
> on one of the check-tcg tests:
>
> $ UBSAN_OPTIONS=print_stacktrace=1:abort_on_error=1:halt_on_error=1 
> ./build/clang/qemu-system-riscv64 -M virt -semihosting -display none -device 
> loader,file=build/clang/tests/tcg/riscv64-softmmu/issue1060
> ../../target/riscv/cpu_helper.c:1805:38: runtime error: shift exponent 63 is 
> too large for 32-bit type 'int'
>     #0 0x55f2dc026703 in riscv_cpu_do_interrupt 
> /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/clang/../../target/riscv/cpu_helper.c:1805:38
>     #1 0x55f2dc3d170e in cpu_handle_exception 
> /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/build/clang/../../accel/tcg/cpu-exec.c:752:9
>
> In this case cause is RISCV_EXCP_SEMIHOST, which is 0x3f.
>
> Use 1ULL instead to ensure that the shift is in range.
>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  target/riscv/cpu_helper.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> index 0a3ead69eab..45806f5ab0f 100644
> --- a/target/riscv/cpu_helper.c
> +++ b/target/riscv/cpu_helper.c
> @@ -1802,10 +1802,10 @@ void riscv_cpu_do_interrupt(CPUState *cs)
>      bool async = !!(cs->exception_index & RISCV_EXCP_INT_FLAG);
>      target_ulong cause = cs->exception_index & RISCV_EXCP_INT_MASK;
>      uint64_t deleg = async ? env->mideleg : env->medeleg;
> -    bool s_injected = env->mvip & (1 << cause) & env->mvien &&
> -        !(env->mip & (1 << cause));
> -    bool vs_injected = env->hvip & (1 << cause) & env->hvien &&
> -        !(env->mip & (1 << cause));
> +    bool s_injected = env->mvip & (1ULL << cause) & env->mvien &&
> +        !(env->mip & (1ULL << cause));
> +    bool vs_injected = env->hvip & (1ULL << cause) & env->hvien &&
> +        !(env->mip & (1ULL << cause));
>      target_ulong tval = 0;
>      target_ulong tinst = 0;
>      target_ulong htval = 0;
> --
> 2.34.1
>
>