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authorMarco Elver <elver@google.com>2023-08-11 18:18:40 +0300
committerKees Cook <keescook@chromium.org>2023-08-16 00:57:25 +0300
commitaebc7b0d8d91bbc69e976909963046bc48bca4fd (patch)
treed9a2b25f46793d9bfd8e64cc5dd8570e4cc5f27d /lib/Makefile
parentb16c42c8fde808b4f047d94f1f2aeda93487670d (diff)
downloadlinux-aebc7b0d8d91bbc69e976909963046bc48bca4fd.tar.xz
list: Introduce CONFIG_LIST_HARDENED
Numerous production kernel configs (see [1, 2]) are choosing to enable CONFIG_DEBUG_LIST, which is also being recommended by KSPP for hardened configs [3]. The motivation behind this is that the option can be used as a security hardening feature (e.g. CVE-2019-2215 and CVE-2019-2025 are mitigated by the option [4]). The feature has never been designed with performance in mind, yet common list manipulation is happening across hot paths all over the kernel. Introduce CONFIG_LIST_HARDENED, which performs list pointer checking inline, and only upon list corruption calls the reporting slow path. To generate optimal machine code with CONFIG_LIST_HARDENED: 1. Elide checking for pointer values which upon dereference would result in an immediate access fault (i.e. minimal hardening checks). The trade-off is lower-quality error reports. 2. Use the __preserve_most function attribute (available with Clang, but not yet with GCC) to minimize the code footprint for calling the reporting slow path. As a result, function size of callers is reduced by avoiding saving registers before calling the rarely called reporting slow path. Note that all TUs in lib/Makefile already disable function tracing, including list_debug.c, and __preserve_most's implied notrace has no effect in this case. 3. Because the inline checks are a subset of the full set of checks in __list_*_valid_or_report(), always return false if the inline checks failed. This avoids redundant compare and conditional branch right after return from the slow path. As a side-effect of the checks being inline, if the compiler can prove some condition to always be true, it can completely elide some checks. Since DEBUG_LIST is functionally a superset of LIST_HARDENED, the Kconfig variables are changed to reflect that: DEBUG_LIST selects LIST_HARDENED, whereas LIST_HARDENED itself has no dependency on DEBUG_LIST. Running netperf with CONFIG_LIST_HARDENED (using a Clang compiler with "preserve_most") shows throughput improvements, in my case of ~7% on average (up to 20-30% on some test cases). Link: https://r.android.com/1266735 [1] Link: https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/blob/main/config [2] Link: https://kernsec.org/wiki/index.php/Kernel_Self_Protection_Project/Recommended_Settings [3] Link: https://googleprojectzero.blogspot.com/2019/11/bad-binder-android-in-wild-exploit.html [4] Signed-off-by: Marco Elver <elver@google.com> Link: https://lore.kernel.org/r/20230811151847.1594958-3-elver@google.com Signed-off-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'lib/Makefile')
-rw-r--r--lib/Makefile2
1 files changed, 1 insertions, 1 deletions
diff --git a/lib/Makefile b/lib/Makefile
index 42d307ade225..110936c9a68b 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -161,7 +161,7 @@ obj-$(CONFIG_BTREE) += btree.o
obj-$(CONFIG_INTERVAL_TREE) += interval_tree.o
obj-$(CONFIG_ASSOCIATIVE_ARRAY) += assoc_array.o
obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o
-obj-$(CONFIG_DEBUG_LIST) += list_debug.o
+obj-$(CONFIG_LIST_HARDENED) += list_debug.o
obj-$(CONFIG_DEBUG_OBJECTS) += debugobjects.o
obj-$(CONFIG_BITREVERSE) += bitrev.o