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From: Mark Rutland <mark.rutland@arm.com>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	Kees Cook <keescook@chromium.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Will Deacon <will@kernel.org>, Jessica Yu <jeyu@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>, Tejun Heo <tj@kernel.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>, bpf <bpf@vger.kernel.org>,
	linux-hardening@vger.kernel.org,
	linux-arch <linux-arch@vger.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-kbuild <linux-kbuild@vger.kernel.org>,
	PCI <linux-pci@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 03/17] mm: add generic __va_function and __pa_function macros
Date: Thu, 25 Mar 2021 10:16:55 +0000	[thread overview]
Message-ID: <20210325101655.GB36570@C02TD0UTHF1T.local> (raw)
In-Reply-To: <CABCJKufRHCb0sjr1tMGCoVMzV-5dKPPn-t8=+ihNFAgTr2k0DA@mail.gmail.com>

On Wed, Mar 24, 2021 at 08:54:18AM -0700, Sami Tolvanen wrote:
> On Wed, Mar 24, 2021 at 12:14 AM Christoph Hellwig <hch@infradead.org> wrote:
> >
> > On Tue, Mar 23, 2021 at 01:39:32PM -0700, Sami Tolvanen wrote:
> > > With CONFIG_CFI_CLANG, the compiler replaces function addresses
> > > in instrumented C code with jump table addresses. This means that
> > > __pa_symbol(function) returns the physical address of the jump table
> > > entry instead of the actual function, which may not work as the jump
> > > table code will immediately jump to a virtual address that may not be
> > > mapped.
> > >
> > > To avoid this address space confusion, this change adds generic
> > > definitions for __va_function and __pa_function, which architectures
> > > that support CFI can override. The typical implementation of the
> > > __va_function macro would use inline assembly to take the function
> > > address, which avoids compiler instrumentation.
> >
> > I think these helper are sensible, but shouldn't they have somewhat
> > less arcane names and proper documentation?
> 
> Good point, I'll add comments in the next version. I thought
> __pa_function would be a fairly straightforward replacement for
> __pa_symbol, but I'm fine with renaming these. Any suggestions for
> less arcane names?

I think dropping 'nocfi' into the name would be clear enough. I think
that given the usual fun with {symbol,module,virt}->phys conversions
it's not worth having the __pa_* form, and we can leave the phys
conversion to the caller that knows where the function lives.

How about we just add `function_nocfi()` ?

Callers can then do `__pa_symbol(function_nocfi(foo))` and similar.

Thanks,
Mark.

  reply	other threads:[~2021-03-25 10:17 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-23 20:39 [PATCH v3 00/17] Add support for Clang CFI Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 01/17] add " Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 02/17] cfi: add __cficanonical Sami Tolvanen
2021-03-24 15:31   ` Rasmus Villemoes
2021-03-24 16:38     ` Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 03/17] mm: add generic __va_function and __pa_function macros Sami Tolvanen
2021-03-24  7:13   ` Christoph Hellwig
2021-03-24 15:54     ` Sami Tolvanen
2021-03-25 10:16       ` Mark Rutland [this message]
2021-03-25 23:17         ` Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 04/17] module: ensure __cfi_check alignment Sami Tolvanen
2021-03-26  4:34   ` Kees Cook
2021-03-29  9:26   ` Jessica Yu
2021-03-23 20:39 ` [PATCH v3 05/17] workqueue: use WARN_ON_FUNCTION_MISMATCH Sami Tolvanen
2021-03-26  4:34   ` Kees Cook
2021-03-23 20:39 ` [PATCH v3 06/17] kthread: " Sami Tolvanen
2021-03-26  4:35   ` Kees Cook
2021-03-23 20:39 ` [PATCH v3 07/17] kallsyms: strip ThinLTO hashes from static functions Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 08/17] bpf: disable CFI in dispatcher functions Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 09/17] treewide: Change list_sort to use const pointers Sami Tolvanen
2021-03-23 21:28   ` Nick Desaulniers
2021-03-24  7:10   ` Christoph Hellwig
2021-03-26  4:35   ` Kees Cook
2021-03-23 20:39 ` [PATCH v3 10/17] lkdtm: use __va_function Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 11/17] psci: use __pa_function for cpu_resume Sami Tolvanen
2021-03-25 10:23   ` Mark Rutland
2021-03-23 20:39 ` [PATCH v3 12/17] arm64: implement __va_function Sami Tolvanen
2021-03-25 10:37   ` Mark Rutland
2021-03-25 23:27     ` Sami Tolvanen
2021-03-26  0:03       ` Peter Collingbourne
2021-03-23 20:39 ` [PATCH v3 13/17] arm64: use __pa_function Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 14/17] arm64: add __nocfi to functions that jump to a physical address Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 15/17] arm64: add __nocfi to __apply_alternatives Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 16/17] KVM: arm64: Disable CFI for nVHE Sami Tolvanen
2021-03-23 20:39 ` [PATCH v3 17/17] arm64: allow CONFIG_CFI_CLANG to be selected Sami Tolvanen

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