On Tue, Jul 27, 2021 at 02:18:58PM -0700, Nathan Chancellor wrote:

On 7/27/2021 1:58 PM, Kees Cook wrote:

quoted

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 <redacted>
---
  security/Kconfig | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/security/Kconfig b/security/Kconfig
index 0ced7fd33e4d..8f0e675e70a4 100644
--- a/security/Kconfig
+++ b/security/Kconfig

@@ -191,6 +191,9 @@ config HARDENED_USERCOPY_PAGESPAN
  config FORTIFY_SOURCE
  	bool "Harden common str/mem functions against buffer overflows"
  	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 !CONFIG_CC_IS_CLANG

Should be !CC_IS_CLANG, Kconfig is hard :)

/me shakes fist at sky

Thank you! Fixed locally. :)

-Kees

quoted

  	help
  	  Detect overflows of buffers in common string and memory functions
  	  where the compiler can determine and validate the buffer sizes.

Cheers,
Nathan

-- 
Kees Cook