Messages in this thread | | | From | Deepak Gupta <> | Date | Thu, 20 Jul 2023 11:42:38 -0700 | Subject | Re: [PATCH v2] riscv: VMAP_STACK overflow detection thread-safe |
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On Thu, Jul 20, 2023 at 11:38 AM Deepak Gupta <debug@rivosinc.com> wrote: > > On Wed, Jul 19, 2023 at 5:18 PM Sami Tolvanen <samitolvanen@google.com> wrote: >> >> Hi Deepak, >> >> On Thu, Nov 24, 2022 at 01:48:45AM -0800, Deepak Gupta wrote: >> > commit 31da94c25aea ("riscv: add VMAP_STACK overflow detection") added >> > support for CONFIG_VMAP_STACK. If overflow is detected, CPU switches to >> > `shadow_stack` temporarily before switching finally to per-cpu >> > `overflow_stack`. >> > >> > If two CPUs/harts are racing and end up in over flowing kernel stack, one >> > or both will end up corrupting each other state because `shadow_stack` is >> > not per-cpu. This patch optimizes per-cpu overflow stack switch by >> > directly picking per-cpu `overflow_stack` and gets rid of `shadow_stack`. >> >> Are you planning on resending this patch? I see it didn't gain much >> traction last time, but this looks like a much cleaner solution for >> selecting the overflow stack than having a `shadow_stack` and calling >> to C to compute the per-CPU offset. The asm_per_cpu macro also would >> come in handy when implementing CONFIG_SHADOW_CALL_STACK, which we'd >> like to have on RISC-V too. > > > I personally like the approach of using percpu because I found it cleaner and easy to maintain. > > There wasn't any willingness to accept that patch because list members / maintainers thought the best way to fix an error prone mechanism is > to introduce another clunky mechanism which is difficult to maintain. So no plan on resending that patch. > > If there is motivation to use the asm_per_cpu macro for other stuff, please feel free to use it from my patch. > I believe it will be handy. > > If there is motivation to accept this patch on the list or provide suggestions on this patch, I can resend it.
Sorry for the last html formatted email. Somehow settings in my gmail got reset and plaintext mode was set to html again.
> > -Deepak > > > >> >> >> Sami
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