Re: [PATCH v3 11/21] exec: Add support for TARGET_TAGGED_ADDRESSES

[Richard Henderson]

On 1/22/21 4:13 AM, Peter Maydell wrote:
> On Fri, 15 Jan 2021 at 22:47, Richard Henderson
> <richard.henderson@linaro.org> wrote:
>>
>> The AArch64 Linux ABI has always enabled TBI, but has historically
>> required that pointer tags be removed before a syscall.  This has
>> changed in the lead-up to ARMv8.5-MTE, in a way that affects the
>> ABI generically and not specifically to MTE.
>>
>> This patch allows the target to indicate that (1) there are tags
>> and (2) whether or not they should be taken into account at the
>> syscall level.
>>
>> Adjust g2h, guest_addr_valid, and guest_range_valid to ignore
>> pointer tags, similar to how TIF_TAGGED_ADDR alters __range_ok
>> in the arm64 kernel source.
>>
>> The prctl syscall is not not yet updated, so this change by itself
>> has no visible effect.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>  include/exec/cpu_ldst.h | 20 +++++++++++++++++---
>>  1 file changed, 17 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/exec/cpu_ldst.h b/include/exec/cpu_ldst.h
>> index e62f4fba00..1df9b93e59 100644
>> --- a/include/exec/cpu_ldst.h
>> +++ b/include/exec/cpu_ldst.h
>> @@ -69,17 +69,31 @@ typedef uint64_t abi_ptr;
>>  #define TARGET_ABI_FMT_ptr "%"PRIx64
>>  #endif
>>
>> +static inline abi_ptr untagged_addr(abi_ptr x)
>> +{
>> +#ifdef TARGET_TAGGED_ADDRESSES
>> +    if (current_cpu) {
>> +        return cpu_untagged_addr(current_cpu, x);
>> +    }
>> +#endif
>> +    return x;
>> +}
> 
> The current_cpu global is a nasty hack and I don't like seeing
> new usages of it. In particular, it's very difficult to
> analyse in what places this will get called when current_cpu is
> NULL and whether it's always OK to not clean the tag in that
> situation.

Well, that'll be a really lot of changes to add cpu/env as an argument to
get_user et al.

Let's see how easily coccinelle can fix em all up for me...


r~