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

[Zong Li]

On Wed, Jun 4, 2025 at 9:06 AM Deepak Gupta <debug at rivosinc.com> wrote:
>
> 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 at rivosinc.com> 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 at rivosinc.com>
> >> >Signed-off-by: Deepak Gupta <debug at rivosinc.com>
> >> >Signed-off-by: Zong Li <zong.li at sifive.com>
> >> >---
> >> >
> >> >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.

Hi Deepak,
I have submitted the v2 patch. Please let me know if further
modifications are required. Thanks
https://lists.infradead.org/pipermail/linux-riscv/2025-June/071483.html

>
> >
> >>
> >> >+                      /* 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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