On Thu, Jul 09, 2026 at 04:15:15PM +0800, Jinjie Ruan wrote:
> On 7/9/2026 3:17 PM, Thomas Weißschuh wrote:
> > On Thu, Jul 09, 2026 at 02:37:05PM +0800, Jinjie Ruan wrote:
> >> On 6/30/2026 11:32 PM, Thomas Weißschuh wrote:
> >>> On Mon, Jun 29, 2026 at 09:06:16PM +0800, Jinjie Ruan wrote:
> > (..)
> >
> >>>> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> >>>> index 592dd8668de4..5a0314a3c26e 100644
> >>>> --- a/arch/arm64/kernel/vdso.c
> >>>> +++ b/arch/arm64/kernel/vdso.c
> >>>> @@ -343,3 +343,19 @@ int arch_setup_additional_pages(struct linux_binprm
> >>>> *bprm, int uses_interp)
> >>>>
> >>>> return ret;
> >>>> }
> >>>> +
> >>>> +bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
> >>>> +{
> >>>> + unsigned long sigtramp;
> >>>> +
> >>>> +#ifdef CONFIG_COMPAT
> >>>> + if (is_compat_task()) {
> >>>> + unsigned long sigpage = (unsigned
> >>>> long)current->mm->context.sigpage;
> >>>> +
> >>>> + return regs->pc >= sigpage && regs->pc < (sigpage +
> >>>> PAGE_SIZE);
> >>>> + }
> >>>> +#endif
> >>>> + sigtramp = (unsigned
> >>>> long)VDSO_SYMBOL(current->mm->context.vdso, sigtramp);
> >>>> +
> >>>> + return regs->pc == (sigtramp + 8);
> >>>
> >>> Instead of hardcoding 'sigtramp + 8' you could add a new label to the
> >>> 'svc #0'
> >>> instruction and use that with VDSO_SYMBOL().
> >>
> >> It seems that the modification of __kernel_rt_sigreturn() is not
> >> recommended
> >
> > For the changes to the object code of the function this is obvious and
> > well explained in the comments.
> >
> > Such a label however would not change the object code of the function.
> > In fact it would not change any bit whatsoever in the final vDSO,
> > save for a new build ID.
>
> Yes, and using labels is easier to maintain than hardcoding offsets
> directly.
>
> Similar to the code below?
Exactly.
(...)
> diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
> index 592dd8668de4..609d7bcd8308 100644
> --- a/arch/arm64/kernel/vdso.c
> +++ b/arch/arm64/kernel/vdso.c
> @@ -343,3 +343,19 @@ int arch_setup_additional_pages(struct linux_binprm
> *bprm, int uses_interp)
>
> return ret;
> }
> +
> +bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
> +{
> + unsigned long sigtramp;
Could be named better now.
> +#ifdef CONFIG_COMPAT
> + if (is_compat_task()) {
> + unsigned long sigpage = (unsigned
> long)current->mm->context.sigpage;
> +
> + return regs->pc >= sigpage && regs->pc < (sigpage +
> PAGE_SIZE);
> + }
> +#endif
> + sigtramp = (unsigned long)VDSO_SYMBOL(current->mm->context.vdso,
> sigreturn_landing_pad);
> +
> + return regs->pc == sigtramp;
> +}
> diff --git a/arch/arm64/kernel/vdso/sigreturn.S
> b/arch/arm64/kernel/vdso/sigreturn.S
> index 0e18729abc3b..8d2d413ff45e 100644
> --- a/arch/arm64/kernel/vdso/sigreturn.S
> +++ b/arch/arm64/kernel/vdso/sigreturn.S
> @@ -73,6 +73,7 @@ SYM_CODE_START(__kernel_rt_sigreturn)
> mov x8, #__NR_rt_sigreturn
> // PLEASE DO NOT MODIFY
> svc #0
> + SYM_INNER_LABEL(__sigreturn_landing_pad, SYM_L_GLOBAL)
> // PLEASE DO NOT MODIFY
> // .cfi_endproc
> SYM_CODE_END(__kernel_rt_sigreturn)
> diff --git a/arch/arm64/kernel/vdso/vdso.lds.S
> b/arch/arm64/kernel/vdso/vdso.lds.S
> index 52314be29191..5fee2927e4c5 100644
> --- a/arch/arm64/kernel/vdso/vdso.lds.S
> +++ b/arch/arm64/kernel/vdso/vdso.lds.S
> @@ -104,6 +104,7 @@ VERSION
> __kernel_clock_gettime;
> __kernel_clock_getres;
> __kernel_getrandom;
> + __sigreturn_landing_pad;
This should not be done. The symbol is not intended to be used by userspace.
> local: *;
> };
> }
> @@ -112,3 +113,4 @@ VERSION
> * Make the sigreturn code visible to the kernel.
> */
> VDSO_sigtramp = __kernel_rt_sigreturn;
> +VDSO_sigreturn_landing_pad = __sigreturn_landing_pad;
