Messages in this thread Patch in this message | | | From | Mark Rutland <> | Subject | [PATCH] kcov: reject open when kernel not instrumented | Date | Wed, 15 Jun 2016 16:49:16 +0100 |
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If the toolchain does not support -fsanitize-coverage=trace-pc, we blat this option from CFLAGS_KCOV, and build the kernel without instrumentation, even if CONFIG_KCOV was selected. However, we still build the rest of the kcov infrastructure, and expose a kcov file under debugfs. This can be confusing, as the kernel will appear to support kcov, yet will never manage to sample any trace PC values. While we do note this fact at build time, this may be missed, and a user may not have access to build logs.
This patch adds an artificial CONFIG symbol, CONFIG_KCOV_CC, that is only set when the toolchain supports -fsanitize-coverage=trace-pc, and hence the kernel is built with instrumentation. When this is not the case, the kernel will return -ENOTSUPP if userspace attempts to open the kcov debugfs file, indicating that kcov functionality is unavailable.
Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Potapenko <glider@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Dmitry Vyukov <dvyukov@google.com> Cc: James Morse <james.morse@arm.com> Cc: Kees Cook <keescook@chromium.org> Cc: Michal Marek <mmarek@suse.com> Cc: linux-kernel@vger.kernel.org --- Makefile | 2 +- kernel/kcov.c | 8 ++++++++ 2 files changed, 9 insertions(+), 1 deletion(-)
As discussed [1] in reply to the arm64 patch.
[1] http://lkml.kernel.org/r/CACT4Y+Z3=juvxBJBXRh5PgE35twFRxg-3iMc-owenONU84x5XQ@mail.gmail.com
Mark.
diff --git a/Makefile b/Makefile index 0f70de6..e6ef260 100644 --- a/Makefile +++ b/Makefile @@ -369,7 +369,7 @@ LDFLAGS_MODULE = CFLAGS_KERNEL = AFLAGS_KERNEL = CFLAGS_GCOV = -fprofile-arcs -ftest-coverage -fno-tree-loop-im -Wno-maybe-uninitialized -CFLAGS_KCOV = -fsanitize-coverage=trace-pc +CFLAGS_KCOV = -fsanitize-coverage=trace-pc -DCONFIG_KCOV_CC # Use USERINCLUDE when you must reference the UAPI directories only. diff --git a/kernel/kcov.c b/kernel/kcov.c index a02f2dd..df2cafd 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -3,6 +3,7 @@ #define DISABLE_BRANCH_PROFILING #include <linux/compiler.h> #include <linux/types.h> +#include <linux/errno.h> #include <linux/file.h> #include <linux/fs.h> #include <linux/mm.h> @@ -160,6 +161,13 @@ static int kcov_open(struct inode *inode, struct file *filep) { struct kcov *kcov; + /* + * CONFIG_KCOV was selected, but the compiler does not support the + * options KCOV requires. + */ + if (!IS_ENABLED(CONFIG_KCOV_CC)) + return -ENOTSUPP; + kcov = kzalloc(sizeof(*kcov), GFP_KERNEL); if (!kcov) return -ENOMEM; -- 1.9.1
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