linux-kernel - Re: [PATCH v2] riscv: VMAP_STACK overflow detection thread-safe

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 24 Jul 2023 09:34:04 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Guo Ren <guoren@...nel.org>
Cc:     Deepak Gupta <debug@...osinc.com>, palmer@...belt.com,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        Jisheng Zhang <jszhang@...nel.org>
Subject: Re: [PATCH v2] riscv: VMAP_STACK overflow detection thread-safe

On Thu, Jul 20, 2023 at 8:06 AM Guo Ren <guoren@...nel.org> wrote:
>
> On Thu, Jul 20, 2023 at 8:19 AM Sami Tolvanen <samitolvanen@...gle.com> wrote:
> >
> > 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 remember we ended up with an atomic lock mechanism instead of percpu
> offset, so what's the benefit of percpu style in overflow_stack path?

The benefit is not needing a separate temporary stack and locks just
to compute the per-CPU offset. With CONFIG_SHADOW_CALL_STACK, we would
also need a "shadow" shadow call stack in this case before calling to
C code, at which point computing the offsets directly in assembly is
just significantly cleaner and without concurrency issues.

Sami