Re: [PATCH v17 15/15] arm64: vdso: Expose sigreturn address on vdso to the kernel

[Thomas Weißschuh]

On Tue, Jul 21, 2026 at 04:18:58PM +0800, Jinjie Ruan wrote:
> Syscall User Dispatch (SUD) must not intercept the signal trampoline
> code, otherwise returning from a signal with a locked selector may
> cause infinite recursion into the signal handler.
> 
> Provide an arm64 implementation of arch_syscall_is_vdso_sigreturn()
> to exclude these sigreturn syscalls from dispatch.
> 
> For native 64-bit tasks, check whether the current PC matches the 'svc #0'
> instruction inside the vDSO sigreturn trampoline (defined in
> arch/arm64/kernel/vdso/sigreturn.S as below).
> 
> 	SYM_CODE_START(__kernel_rt_sigreturn)
> 		mov     x8, #__NR_rt_sigreturn
> 		svc     #0
> 	SYM_CODE_END(__kernel_rt_sigreturn)

With the new label this code snippet here shouldnt be needed anymore.

> For COMPAT tasks, verify that the instruction falls within the dedicated
> 'sigpage' range, since compat signal handlers use this architecture-
> specific page (not the vDSO) for their return trampoline. This prevents
> SUD from incorrectly dispatching syscalls issued during signal return.
> 
> Suggested-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> Suggested-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
> Suggested-by: kemal <kmal@xxxxxxx>
> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
> ---
>  arch/arm64/Kconfig                 |  1 +
>  arch/arm64/include/asm/elf.h       |  1 +
>  arch/arm64/kernel/vdso.c           | 16 ++++++++++++++++
>  arch/arm64/kernel/vdso/sigreturn.S |  1 +
>  arch/arm64/kernel/vdso/vdso.lds.S  |  1 +
>  5 files changed, 20 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index aea686dce3d5..a41d2b593899 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -86,6 +86,7 @@ config ARM64
>  	select ARCH_SUPPORTS_SCHED_SMT
>  	select ARCH_SUPPORTS_SCHED_CLUSTER
>  	select ARCH_SUPPORTS_SCHED_MC
> +	select ARCH_SUPPORTS_SYSCALL_USER_DISPATCH

>From the subject and description I would not have expected this to be in here.
Split into its own patch?

>  	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
>  	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION if COMPAT
>  	select ARCH_WANT_DEFAULT_BPF_JIT

(...)

For the rest:

Reviewed-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>


Thomas