On Mon, Feb 10, 2025 at 09:26:53AM -0800, Andrii Nakryiko wrote:

On Sun, Feb 9, 2025 at 2:05 PM 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/#m9d416df341b... Cc: Kees Cook kees@kernel.org Cc: Eyal Birger eyal.birger@gmail.com Cc: stable@vger.kernel.org Reported-by: Jann Horn jannh@google.com Signed-off-by: Jiri Olsa jolsa@kernel.org

---

arch/x86/kernel/uprobes.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c index 5a952c5ea66b..109d6641a1b3 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 == -1)
  

slight nit: mixing -1 and unsigned long looks sloppy. Maybe let's add something like

#define UPROBE_NO_TRAMPOLINE_VADDR ((unsigned long)-1)

and return that from uprobe_get_trampoline_vaddr()?

ok, will add that

thanks, jirka

...

•           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