* Re: [RFC PATCH 0/9] arm64: use unwind data on GCC for shadow call stack
[not found] <20211013152243.2216899-1-ardb@kernel.org>
@ 2021-10-13 18:01 ` Nick Desaulniers
0 siblings, 0 replies; only message in thread
From: Nick Desaulniers @ 2021-10-13 18:01 UTC (permalink / raw)
To: Ard Biesheuvel
Cc: linux-arm-kernel, linux-hardening, mark.rutland, catalin.marinas,
will, Kees Cook, Sami Tolvanen, Fangrui Song, Dan Li,
linux-toolchains
On Wed, Oct 13, 2021 at 8:22 AM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> This series is a proof of concept implementation of using unwind tables
> to locate PACIASP/AUTIASP instructions in the code, and patching them
> into shadow call stack pushes/pops at boot time if the platform in
> question does not support pointer authentication in hardware. This way,
> the overhead of the shadow call stack is only imposed if it actually
> gives any benefit. It also means that the compiler does not need to
> generate the code, so this works with GCC as well.
>
> In fact, it only works with GCC at the moment, as Clang does not seem to
> implement the DW_CFA_negate_ra_state correctly, which is emitted after
> each PACIASP or AUTIASP instruction (Clang only does the former).
> However, GCC does not appear to get it quite right either, as it emits
> the directive in the wrong place in some cases (but in a way that can be
> worked around).
Can we work on getting bug reports to the compiler vendors? Then we
can have something free of workarounds, and more toolchain portable.
>
> Note that this only implements it for the core kernel. Modules should be
> straight-forward, and most of the code can be reused. Also, the
> transformation is applied unconditionally, even if the hardware does
> implement PAC, but this does not really matter for a PoC.
>
> One obvious downside is the size of the unwind tables (3 MiB for
> defconfig), although there are plenty of use cases where this does not
> really matters (and I haven't checked the compressed size). However,
> there may be other reasons why we'd want to have access to these unwind
> tables (reliable stack traces), so this will need to be discussed before
> I intend to take this any further.
>
> Cc: Kees Cook <keescook@google.com>
> Cc: Sami Tolvanen <samitolvanen@google.com>
> Cc: Fangrui Song <maskray@google.com>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Dan Li <ashimida@linux.alibaba.com>
>
> Ard Biesheuvel (9):
> arm64: assembler: enable PAC for non-leaf assembler routines
> arm64: cache: use ALIAS version of linkage macros for local aliases
> arm64: crypto: avoid overlapping linkage definitions for AES-CBC
> arm64: aes-neonbs: move frame pop to end of function
> arm64: chacha-neon: move frame pop forward
> arm64: smccc: create proper stack frames for HVC/SMC calls
> arm64: assembler: add unwind annotations to frame push/pop macros
> arm64: unwind: add asynchronous unwind tables to the kernel proper
> arm64: implement dynamic shadow call stack for GCC
>
> Makefile | 4 +-
> arch/Kconfig | 4 +-
> arch/arm64/Kconfig | 11 +-
> arch/arm64/Makefile | 7 +-
> arch/arm64/crypto/aes-modes.S | 4 +-
> arch/arm64/crypto/aes-neonbs-core.S | 8 +-
> arch/arm64/crypto/chacha-neon-core.S | 9 +-
> arch/arm64/include/asm/assembler.h | 32 ++-
> arch/arm64/include/asm/linkage.h | 16 +-
> arch/arm64/kernel/Makefile | 2 +
> arch/arm64/kernel/head.S | 3 +
> arch/arm64/kernel/patch-scs.c | 223 ++++++++++++++++++++
> arch/arm64/kernel/smccc-call.S | 40 ++--
> arch/arm64/kernel/vmlinux.lds.S | 20 ++
> arch/arm64/mm/cache.S | 8 +-
> drivers/firmware/efi/libstub/Makefile | 1 +
> 16 files changed, 347 insertions(+), 45 deletions(-)
> create mode 100644 arch/arm64/kernel/patch-scs.c
>
> --
> 2.30.2
>
--
Thanks,
~Nick Desaulniers
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