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Date: Fri, 11 Dec 2020 11:32:33 -0800
From: Kees Cook <keescook@...omium.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>, Will Deacon <will@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
clang-built-linux@...glegroups.com,
kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH v9 06/16] kbuild: lto: add a default list of used symbols
On Fri, Dec 11, 2020 at 10:46:23AM -0800, Sami Tolvanen wrote:
> With CONFIG_LTO_CLANG, LLVM bitcode has not yet been compiled into a
> binary when the .mod files are generated, which means they don't yet
> contain references to certain symbols that will be present in the final
> binaries. This includes intrinsic functions, such as memcpy, memmove,
> and memset [1], and stack protector symbols [2]. This change adds a
> default symbol list to use with CONFIG_TRIM_UNUSED_KSYMS when Clang's
> LTO is used.
>
> [1] https://llvm.org/docs/LangRef.html#standard-c-c-library-intrinsics
> [2] https://llvm.org/docs/LangRef.html#llvm-stackprotector-intrinsic
>
> Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
> ---
> init/Kconfig | 1 +
> scripts/lto-used-symbollist | 5 +++++
> 2 files changed, 6 insertions(+)
> create mode 100644 scripts/lto-used-symbollist
>
> diff --git a/init/Kconfig b/init/Kconfig
> index 0872a5a2e759..e88c919c1bf1 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -2297,6 +2297,7 @@ config TRIM_UNUSED_KSYMS
> config UNUSED_KSYMS_WHITELIST
> string "Whitelist of symbols to keep in ksymtab"
> depends on TRIM_UNUSED_KSYMS
> + default "scripts/lto-used-symbollist" if LTO_CLANG
> help
> By default, all unused exported symbols will be un-exported from the
> build when TRIM_UNUSED_KSYMS is selected.
> diff --git a/scripts/lto-used-symbollist b/scripts/lto-used-symbollist
> new file mode 100644
> index 000000000000..38e7bb9ebaae
> --- /dev/null
> +++ b/scripts/lto-used-symbollist
> @@ -0,0 +1,5 @@
> +memcpy
> +memmove
> +memset
> +__stack_chk_fail
> +__stack_chk_guard
> --
> 2.29.2.576.ga3fc446d84-goog
>
bikeshed: Should this filename use some kind of extension, like
lto-user-symbols.txt or .list, to make it more human-friendly?
--
Kees Cook
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