Re: [PATCH v16 18/18] arm64: vdso: Expose sigreturn address on vdso to the kernel

[Ada Couprie Diaz <ada.coupriediaz@arm.com>]

Hi Jinjie,

On 29/06/2026 14:06, Jinjie Ruan wrote:

> Syscall User Dispatch (SUD) requires the signal trampoline code to not be
> intercepted. This is necessary to support returning with a locked selector
> while avoiding infinite recursion back into the signal handler.

Thanks for splitting this out, I find it is much clearer that way !

However, this should definitely be earlier in the series
As I mentioned in my comment in v15, Syscall User Dispatch only depends
on `CONFIG_GENERIC_ENTRY`, so enabling generic entry for arm64 in patch 16
also enables Syscall User Dispatch.

Given that this series adds a weak default function returning false for
`arch_syscall_is_vdso_sigreturn()` before enabling generic entry for arm64
in patch 16,  patch 16 and 17 have a potentially broken SUD enabled,
as we do not check for those sigreturns yet.

I think shuffling this patch back just before converting to generic entry
should be OK !

>
> Implement arch_syscall_is_vdso_sigreturn() for arm64 to support this
> exclusion mechanism. For native 64-bit tasks, it checks whether the current
> PC matches the 'svc #0' instruction inside the vDSO sigreturn trampoline.
>
> 	SYM_CODE_START(__kernel_rt_sigreturn)
> 	        mov     x8, #__NR_rt_sigreturn
> 	        svc     #0
> 	SYM_CODE_END(__kernel_rt_sigreturn)
Maybe add `arch/arm64/kernel/vdso/sigreturn.S` to mention where
this snippet comes from ?
>
> For COMPAT tasks, it verifies if the instruction falls within
> the architecture's 'sigpage' range, allowing the kernel to safely bypass
> dispatching syscalls originating from these areas back to userspace.
I think this might benefit from a bit more details or clarity on the "why"
of the COMPAT handling : there is a vDSO page for COMPAT tasks, but
COMPAT signal handlers have their own dedicated page, `sigpage`,
which serves the same purpose and is handled similarly, so it needs
to be checked as well.

Hopefully that is correct... Would you find that relevant information to 
add ?
Pinging @Kevin Brodsky on that as well.

> Suggested-by: Kevin Brodsky <kevin.brodsky@arm.com>
> Suggested-by: kemal <kmal@cock.li>
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
> ---
>   arch/arm64/include/asm/elf.h |  1 +
>   arch/arm64/kernel/vdso.c     | 16 ++++++++++++++++
>   2 files changed, 17 insertions(+)

Otherwise this looks good to me, great to have more context with the 
change !

Thanks,
Ada