linux-kernel - Re: [PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check

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Message-ID: <CAADnVQJ05xkXw+c_T1qB+ECUqO5sJxDVJ3bypjS3KSQCTJb-1g@mail.gmail.com>
Date: Tue, 11 Feb 2025 08:52:34 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Jiri Olsa <jolsa@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Oleg Nesterov <oleg@...hat.com>, 
	Peter Zijlstra <peterz@...radead.org>, Andrii Nakryiko <andrii@...nel.org>, Kees Cook <kees@...nel.org>, 
	Eyal Birger <eyal.birger@...il.com>, stable <stable@...r.kernel.org>, 
	Jann Horn <jannh@...gle.com>, LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, 
	X86 ML <x86@...nel.org>, bpf <bpf@...r.kernel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Andy Lutomirski <luto@...nel.org>, 
	Deepak Gupta <debug@...osinc.com>, Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check

On Tue, Feb 11, 2025 at 8:48 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Tue, Feb 11, 2025 at 3:16 AM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > Jann reported [1] possible issue when trampoline_check_ip returns
> > address near the bottom of the address space that is allowed to
> > call into the syscall if uretprobes are not set up.
> >
> > Though the mmap minimum address restrictions will typically prevent
> > creating mappings there, let's make sure uretprobe syscall checks
> > for that.
> >
> > [1] https://lore.kernel.org/bpf/202502081235.5A6F352985@keescook/T/#m9d416df341b8fbc11737dacbcd29f0054413cbbf
> > Cc: Kees Cook <kees@...nel.org>
> > Cc: Eyal Birger <eyal.birger@...il.com>
> > Cc: stable@...r.kernel.org
> > Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
> > Reported-by: Jann Horn <jannh@...gle.com>
> > Reviewed-by: Oleg Nesterov <oleg@...hat.com>
> > Reviewed-by: Kees Cook <kees@...nel.org>
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> > v2 changes:
> > - adding UPROBE_NO_TRAMPOLINE_VADDR macro (Andrii)
> > - rebased on top of perf/core
> >
> >  arch/x86/kernel/uprobes.c | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> > index 5a952c5ea66b..e8d3c59aa9f7 100644
> > --- a/arch/x86/kernel/uprobes.c
> > +++ b/arch/x86/kernel/uprobes.c
> > @@ -357,19 +357,25 @@ void *arch_uprobe_trampoline(unsigned long *psize)
> >         return &insn;
> >  }
> >
> > -static unsigned long trampoline_check_ip(void)
> > +static unsigned long trampoline_check_ip(unsigned long tramp)
> >  {
> > -       unsigned long tramp = uprobe_get_trampoline_vaddr();
> > -
> >         return tramp + (uretprobe_syscall_check - uretprobe_trampoline_entry);
> >  }
> >
> > +#define UPROBE_NO_TRAMPOLINE_VADDR ((unsigned long)-1)

If you respin anyway maybe use ~0UL instead?
In the above and in
uprobe_get_trampoline_vaddr(),
since

unsigned long trampoline_vaddr = -1;

looks odd too.