From: Ard Biesheuvel <ardb@kernel.org>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: Linus Walleij <linus.walleij@linaro.org>,
Sami Tolvanen <samitolvanen@google.com>,
Kees Cook <keescook@chromium.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev
Subject: Re: [PATCH v8 0/9] CFI for ARM32 using LLVM
Date: Mon, 29 Apr 2024 16:54:39 +0200 [thread overview]
Message-ID: <CAMj1kXG_oLtPMEhnnpQjJUSgFnJv-rP_yC-BNJRr+aC5eycnWA@mail.gmail.com> (raw)
In-Reply-To: <Zi+e9M/f5b/Sto9H@shell.armlinux.org.uk>
On Mon, 29 Apr 2024 at 15:22, Russell King (Oracle)
<linux@armlinux.org.uk> wrote:
>
> I've applied this to a separate branch, and it should be in
> linux-next by tomorrow.
>
> As mentioned today on a previous iteration of the patch series,
> I'm not all that happy with the introduction of delay-inducing
> branches to solve CFI issues especially on the early CPUs where
> a branch causes the CPUs pipeline to be flushed - thus making
> branches expensive.
>
> Can we make these branches conditional on the use of CFI?
>
> Didn't Ard mention there was a way to do this using symbol aliases?
>
Yes, but only if the prototypes are identical. Not sure why Linus
decided to keep this separate, but 9386/2 implements this for
flush_user_cache_all() vs. flush_kern_cache_all().
For coherent_user_range() vs. coherent_kern_range(), the return type
is different (void vs int)
So we could either make coherent_kern_range() return int as well, or
alternatively, we could emit the branch instructions only when CFI is
enabled (as in that case, SYM_TYPED_FUNC_START() expands to something
that prevents a fall through)
E.g.,
--- a/arch/arm/mm/cache-v4wt.S
+++ b/arch/arm/mm/cache-v4wt.S
@@ -108,7 +108,9 @@ SYM_FUNC_END(v4wt_flush_user_cache_range)
* - end - virtual end address
*/
SYM_TYPED_FUNC_START(v4wt_coherent_kern_range)
+#ifdef CONFIG_CFI_CLANG
b v4wt_coherent_user_range
+#endif
SYM_FUNC_END(v4wt_coherent_kern_range)
/*
AFAICT, SYM_TYPED_FUNC_START() does not prevent a fall through if
CFI_CLANG is disabled, but someone should double check.
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next prev parent reply other threads:[~2024-04-29 14:55 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-23 7:19 [PATCH v8 0/9] CFI for ARM32 using LLVM Linus Walleij
2024-04-23 7:19 ` [PATCH v8 1/9] ARM: mm: Make tlbflush routines CFI safe Linus Walleij
2024-04-23 7:19 ` [PATCH v8 3/9] ARM: mm: Use symbol alias for two cache functions Linus Walleij
2024-04-23 7:19 ` [PATCH v8 4/9] ARM: mm: Rewrite cacheflush vtables in CFI safe C Linus Walleij
2024-04-23 7:19 ` [PATCH v8 5/9] ARM: mm: Type-annotate all per-processor assembly routines Linus Walleij
2024-04-23 7:19 ` [PATCH v8 6/9] ARM: mm: Define prototypes for all per-processor calls Linus Walleij
2024-04-23 7:19 ` [PATCH v8 7/9] ARM: lib: Annotate loop delay instructions for CFI Linus Walleij
2024-04-23 7:19 ` [PATCH v8 8/9] ARM: hw_breakpoint: Handle CFI breakpoints Linus Walleij
2024-04-23 7:19 ` [PATCH v8 9/9] ARM: Support CLANG CFI Linus Walleij
2024-04-29 13:21 ` [PATCH v8 0/9] CFI for ARM32 using LLVM Russell King (Oracle)
2024-04-29 14:54 ` Ard Biesheuvel [this message]
2024-04-29 15:06 ` Sami Tolvanen
2024-04-30 7:43 ` Linus Walleij
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