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fortify: Explicitly disable Clang support

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Clang has never correctly compiled the FORTIFY_SOURCE defenses due to
a couple bugs:

	Eliding inlines with matching __builtin_* names
	https://bugs.llvm.org/show_bug.cgi?id=50322

	Incorrect __builtin_constant_p() of some globals
	https://bugs.llvm.org/show_bug.cgi?id=41459

In the process of making improvements to the FORTIFY_SOURCE defenses, the
first (silent) bug (coincidentally) becomes worked around, but exposes
the latter which breaks the build. As such, Clang must not be used with
CONFIG_FORTIFY_SOURCE until at least latter bug is fixed (in Clang 13),
and the fortify routines have been rearranged.

Update the Kconfig to reflect the reality of the current situation.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/lkml/CAKwvOd=A+ueGV2ihdy5GtgR2fQbcXjjAtVxv3=cPjffpebZB7A@mail.gmail.com
This commit is contained in:
Kees Cook 2021-05-12 21:51:10 -07:00
parent c430f60036
commit a52f8a59ae
1 changed files with 3 additions and 0 deletions
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security/Kconfig
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@ -191,6 +191,9 @@ config HARDENED_USERCOPY_PAGESPAN
config FORTIFY_SOURCE config FORTIFY_SOURCE
bool "Harden common str/mem functions against buffer overflows" bool "Harden common str/mem functions against buffer overflows"
depends on ARCH_HAS_FORTIFY_SOURCE depends on ARCH_HAS_FORTIFY_SOURCE
# https://bugs.llvm.org/show_bug.cgi?id=50322
# https://bugs.llvm.org/show_bug.cgi?id=41459
depends on !CC_IS_CLANG
help help
Detect overflows of buffers in common string and memory functions Detect overflows of buffers in common string and memory functions
where the compiler can determine and validate the buffer sizes. where the compiler can determine and validate the buffer sizes.