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[PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check

Jiri Olsa posted 1 patch 10 months, 1 week ago
There is a newer version of this series
arch/x86/kernel/uprobes.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
[PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check
Posted by Jiri Olsa 10 months, 1 week ago 
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@kernel.org>
Cc: Eyal Birger <eyal.birger@gmail.com>
Cc: stable@vger.kernel.org
Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
Reported-by: Jann Horn <jannh@google.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.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)
+
 SYSCALL_DEFINE0(uretprobe)
 {
 	struct pt_regs *regs = task_pt_regs(current);
-	unsigned long err, ip, sp, r11_cx_ax[3];
+	unsigned long err, ip, sp, r11_cx_ax[3], tramp;
+
+	/* If there's no trampoline, we are called from wrong place. */
+	tramp = uprobe_get_trampoline_vaddr();
+	if (tramp == UPROBE_NO_TRAMPOLINE_VADDR)
+		goto sigill;
 
-	if (regs->ip != trampoline_check_ip())
+	/* Make sure the ip matches the only allowed sys_uretprobe caller. */
+	if (regs->ip != trampoline_check_ip(tramp))
 		goto sigill;
 
 	err = copy_from_user(r11_cx_ax, (void __user *)regs->sp, sizeof(r11_cx_ax));
-- 
2.48.1
Re: [PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check
Posted by Andrii Nakryiko 10 months, 1 week ago 
On Tue, Feb 11, 2025 at 3:16 AM Jiri Olsa <jolsa@kernel.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@kernel.org>
> Cc: Eyal Birger <eyal.birger@gmail.com>
> Cc: stable@vger.kernel.org
> Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
> Reported-by: Jann Horn <jannh@google.com>
> Reviewed-by: Oleg Nesterov <oleg@redhat.com>
> Reviewed-by: Kees Cook <kees@kernel.org>
> Signed-off-by: Jiri Olsa <jolsa@kernel.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)
> +
>  SYSCALL_DEFINE0(uretprobe)
>  {
>         struct pt_regs *regs = task_pt_regs(current);
> -       unsigned long err, ip, sp, r11_cx_ax[3];
> +       unsigned long err, ip, sp, r11_cx_ax[3], tramp;
> +
> +       /* If there's no trampoline, we are called from wrong place. */
> +       tramp = uprobe_get_trampoline_vaddr();
> +       if (tramp == UPROBE_NO_TRAMPOLINE_VADDR)
> +               goto sigill;
>
> -       if (regs->ip != trampoline_check_ip())
> +       /* Make sure the ip matches the only allowed sys_uretprobe caller. */
> +       if (regs->ip != trampoline_check_ip(tramp))
>                 goto sigill;
>

LGTM. I don't know if that would make any difference, but I'd sprinkle
unlikely() around these two conditions to make sure they don't
interfere with instruction flow much

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>         err = copy_from_user(r11_cx_ax, (void __user *)regs->sp, sizeof(r11_cx_ax));
> --
> 2.48.1
>
Re: [PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check
Posted by Alexei Starovoitov 10 months, 1 week ago 
On Tue, Feb 11, 2025 at 8:48 AM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Tue, Feb 11, 2025 at 3:16 AM Jiri Olsa <jolsa@kernel.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@kernel.org>
> > Cc: Eyal Birger <eyal.birger@gmail.com>
> > Cc: stable@vger.kernel.org
> > Fixes: ff474a78cef5 ("uprobe: Add uretprobe syscall to speed up return probe")
> > Reported-by: Jann Horn <jannh@google.com>
> > Reviewed-by: Oleg Nesterov <oleg@redhat.com>
> > Reviewed-by: Kees Cook <kees@kernel.org>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.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.
Re: [PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check
Posted by Oleg Nesterov 10 months, 1 week ago 
On 02/11, Alexei Starovoitov wrote:
>
> > > +#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;

... or -1ul in both cases.

I agree, UPROBE_NO_TRAMPOLINE_VADDR has a single user, looks
a bit strange...

Oleg.
Re: [PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check
Posted by Masami Hiramatsu (Google) 10 months, 1 week ago 
On Tue, 11 Feb 2025 17:59:41 +0100
Oleg Nesterov <oleg@redhat.com> wrote:

> On 02/11, Alexei Starovoitov wrote:
> >
> > > > +#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;
> 
> ... or -1ul in both cases.
> 
> I agree, UPROBE_NO_TRAMPOLINE_VADDR has a single user, looks
> a bit strange...

I think both this function and uprobe_get_trampoline_vaddr()
should use the same macro as a token.
(and ~0UL is a bit more comfortable for me too :) )

----
unsigned long uprobe_get_trampoline_vaddr(void)
{
	struct xol_area *area;
	unsigned long trampoline_vaddr = -1;
----

Thank you,

> 
> Oleg.
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>
Re: [PATCHv2 perf/core] uprobes: Harden uretprobe syscall trampoline check
Posted by Jiri Olsa 10 months, 1 week ago 
On Wed, Feb 12, 2025 at 01:05:09PM +0900, Masami Hiramatsu wrote:
> On Tue, 11 Feb 2025 17:59:41 +0100
> Oleg Nesterov <oleg@redhat.com> wrote:
> 
> > On 02/11, Alexei Starovoitov wrote:
> > >
> > > > > +#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;
> > 
> > ... or -1ul in both cases.
> > 
> > I agree, UPROBE_NO_TRAMPOLINE_VADDR has a single user, looks
> > a bit strange...
> 
> I think both this function and uprobe_get_trampoline_vaddr()
> should use the same macro as a token.
> (and ~0UL is a bit more comfortable for me too :) )
> 
> ----
> unsigned long uprobe_get_trampoline_vaddr(void)
> {
> 	struct xol_area *area;
> 	unsigned long trampoline_vaddr = -1;
> ----


sounds good, I'll send new version with change below if there
are no objections

thanks,
jirka


---
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 5a952c5ea66b..015b2a6bac11 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -357,19 +357,23 @@ 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);
 }
 
 SYSCALL_DEFINE0(uretprobe)
 {
 	struct pt_regs *regs = task_pt_regs(current);
-	unsigned long err, ip, sp, r11_cx_ax[3];
+	unsigned long err, ip, sp, r11_cx_ax[3], tramp;
+
+	/* If there's no trampoline, we are called from wrong place. */
+	tramp = uprobe_get_trampoline_vaddr();
+	if (tramp == UPROBE_NO_TRAMPOLINE_VADDR)
+		goto sigill;
 
-	if (regs->ip != trampoline_check_ip())
+	/* Make sure the ip matches the only allowed sys_uretprobe caller. */
+	if (regs->ip != trampoline_check_ip(tramp))
 		goto sigill;
 
 	err = copy_from_user(r11_cx_ax, (void __user *)regs->sp, sizeof(r11_cx_ax));
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index b1df7d792fa1..a6bec560bdbc 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -39,6 +39,8 @@ struct page;
 
 #define MAX_URETPROBE_DEPTH		64
 
+#define UPROBE_NO_TRAMPOLINE_VADDR	(~0UL)
+
 struct uprobe_consumer {
 	/*
 	 * handler() can return UPROBE_HANDLER_REMOVE to signal the need to
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 2ca797cbe465..e8af2f75b094 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -2160,8 +2160,8 @@ void uprobe_copy_process(struct task_struct *t, unsigned long flags)
  */
 unsigned long uprobe_get_trampoline_vaddr(void)
 {
+	unsigned long trampoline_vaddr = UPROBE_NO_TRAMPOLINE_VADDR;
 	struct xol_area *area;
-	unsigned long trampoline_vaddr = -1;
 
 	/* Pairs with xol_add_vma() smp_store_release() */
 	area = READ_ONCE(current->mm->uprobes_state.xol_area); /* ^^^ */

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