Re: [PATCH] riscv: traps: handle uprobe event in software-check exception

[Deepak Gupta]

On Tue, Jun 03, 2025 at 09:48:08AM +0800, Zong Li wrote:
> On Tue, Jun 3, 2025 at 12:50 AM Deepak Gupta <debug@xxxxxxxxxxxx> wrote:
> > Hi Zong,
> >
> > Thanks for taking the initiative for making cfi work with uprobe.
> > And sorry for not noticing the patch earlier.
> > Few comments inline.
> >
> >
> > On Fri, Mar 14, 2025 at 05:26:14PM +0800, Zong Li wrote:
> > >Handle the uprobe event first before handling the CFI violation in
> > >software-check exception handler. Because when the landing pad is
> > >activated, if the uprobe point is set at the lpad instruction at
> > >the beginning of a function, the system triggers a software-check
> > >exception instead of an ebreak exception due to the exception
> > >priority, then uprobe can't work successfully.
> > >
> > >Co-developed-by: Deepak Gupta <debug@xxxxxxxxxxxx>
> > >Signed-off-by: Deepak Gupta <debug@xxxxxxxxxxxx>
> > >Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
> > >---
> > >
> > >This patch is based on top of the following series
> > >[PATCH v11 00/27] riscv control-flow integrity for usermode
> > >
> > > arch/riscv/kernel/traps.c | 9 ++++++---
> > > 1 file changed, 6 insertions(+), 3 deletions(-)
> > >
> > >diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> > >index 3f7709f4595a..ef5a92111ee1 100644
> > >--- a/arch/riscv/kernel/traps.c
> > >+++ b/arch/riscv/kernel/traps.c
> > >@@ -386,9 +386,12 @@ asmlinkage __visible __trap_section void do_trap_software_check(struct pt_regs *
> > >       if (user_mode(regs)) {
> > >               irqentry_enter_from_user_mode(regs);
> > >
> > >-              /* not a cfi violation, then merge into flow of unknown trap handler */
> > >-              if (!handle_user_cfi_violation(regs))
> > >-                      do_trap_unknown(regs);
> > >+              /* handle uprobe event frist */
> > >+              if (!probe_breakpoint_handler(regs)) {
> >
> > If task has uprobe enabled and there is a cfi violation due to mismatch in
> > return address on shadow stack and regular stack, then it would be a cfi
> > bypass, right?
> > Perhaps we should be doing this only when we match that sw check exception
> > is due to forward cfi violation?
> >
> > Do you agree?
>
> Yes, let me add a condition for forward cfi violation here. Thanks for
> pointing it out.

Cool, I'll send out another revision for my cfi series this week.
If you send out your uprobe fix, I can include it in my patchset.

> > >+                      /* not a cfi violation, then merge into flow of unknown trap handler */
> > >+                      if (!handle_user_cfi_violation(regs))
> > >+                              do_trap_unknown(regs);
> > >+              }
> > >
> > >               irqentry_exit_to_user_mode(regs);
> > >       } else {
> > >--
> > >2.17.1
> > >
> >
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