The 06/05/2020 17:51, Szabolcs Nagy wrote:
> The handler argument must not be signed since that may come from
> outside the current module and exposing signed addresses is a pointer
> ABI break. (The signed address also may not be representable as void *
> which is why pac-ret is currently broken on ilp32.)
>
> There is no point protecting the eh return path with pointer auth
> since arbitrary target can be reached with the instruction sequence
> in the caller function anyway, however this is a big hammer solution
> that turns off pac-ret for the caller completely not just on the eh
> return path.
>
> 2020-06-04 Szabolcs Nagy <[email protected]>
>
> * config/aarch64/aarch64.c (aarch64_return_address_signing_enabled):
> Disable return address signing if __builtin_eh_return is used.
ping.
this fixes a correctness bug in pac-ret, tested
on aarch64, with only the following regressions:
FAIL: gcc.target/aarch64/return_address_sign_1.c scan-assembler-times autiasp 4
FAIL: gcc.target/aarch64/return_address_sign_1.c scan-assembler-times paciasp 4
FAIL: gcc.target/aarch64/return_address_sign_b_1.c scan-assembler-times autibsp
4
FAIL: gcc.target/aarch64/return_address_sign_b_1.c scan-assembler-times pacibsp
4
which can be fixed by
-/* { dg-final { scan-assembler-times "autiasp" 4 } } */
-/* { dg-final { scan-assembler-times "paciasp" 4 } } */
+/* { dg-final { scan-assembler-times "autiasp" 3 } } */
+/* { dg-final { scan-assembler-times "paciasp" 3 } } */
since __builtin_eh_return path no longer uses pac/aut.
> ---
> gcc/config/aarch64/aarch64.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index 6a2f85c4af7..d9557f7c0a2 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -6954,6 +6954,10 @@ aarch64_return_address_signing_enabled (void)
> /* This function should only be called after frame laid out. */
> gcc_assert (cfun->machine->frame.laid_out);
>
> + /* TODO: Big hammer handling of __builtin_eh_return. */
> + if (crtl->calls_eh_return)
> + return false;
> +
> /* If signing scope is AARCH64_FUNCTION_NON_LEAF, we only sign a leaf
> function
> if its LR is pushed onto stack. */
> return (aarch64_ra_sign_scope == AARCH64_FUNCTION_ALL
> --
> 2.17.1
>
--
