Re: [PATCH] seccomp: passthrough uretprobe systemcall without filtering

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On Fri, 17 Jan 2025 02:39:28 +0100
Oleg Nesterov <oleg@xxxxxxxxxx> wrote:

> On 01/16, Eyal Birger wrote:
> >
> > Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
> > Reported-by: Rafael Buchbinder <rafi@xxxxxx>
> > Link: https://lore.kernel.org/lkml/CAHsH6Gs3Eh8DFU0wq58c_LF8A4_+o6z456J7BidmcVY2AqOnHQ@xxxxxxxxxxxxxx/
> > Cc: stable@xxxxxxxxxxxxxxx
> ...
> > @@ -1359,6 +1359,11 @@ int __secure_computing(const struct seccomp_data *sd)
> >  	this_syscall = sd ? sd->nr :
> >  		syscall_get_nr(current, current_pt_regs());
> >
> > +#ifdef CONFIG_X86_64
> > +	if (unlikely(this_syscall == __NR_uretprobe) && !in_ia32_syscall())
> > +		return 0;
> > +#endif
> 
> Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> 
> 
> A note for the seccomp maintainers...
> 
> I don't know what do you think, but I agree in advance that the very fact this
> patch adds "#ifdef CONFIG_X86_64" into __secure_computing() doesn't look nice.
> 

Indeed. in_ia32_syscall() depends arch/x86 too.
We can add an inline function like;

``` uprobes.h
static inline bool is_uprobe_syscall(int syscall)
{
	// arch_is_uprobe_syscall check can be replaced by Kconfig,
	// something like CONFIG_ARCH_URETPROBE_SYSCALL.
#ifdef arch_is_uprobe_syscall
	return arch_is_uprobe_syscall(syscall)
#else
	return false;
#endif
}
```
and 
``` arch/x86/include/asm/uprobes.h
#define arch_is_uprobe_syscall(syscall) \
	(IS_ENABLED(CONFIG_X86_64) && syscall == __NR_uretprobe && !in_ia32_syscall())
```

> The problem is that we need a simple patch for -stable which fixes the real
> problem. We can cleanup this logic later, I think.

Hmm, at least we should make it is_uprobe_syscall() in uprobes.h so that
do not pollute the seccomp subsystem with #ifdef.

Thank you,



> 
> Oleg.
> 


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>