On Mon, May 11, 2026 at 06:14:27AM -0700, Breno Leitao wrote:
helo Sasha,
First of all, Thanks for this feature, this is useful to me, and I am
interested in it. Feel free to copy me and I can test the next revisions
On Fri, May 08, 2026 at 03:57:48PM -0400, Sasha Levin wrote:
+config KILLSWITCH
+ bool "Killswitch: short-circuit a kernel function as a CVE mitigation"
+ depends on SECURITYFS
+ depends on KPROBES && HAVE_KPROBES_ON_FTRACE
+ depends on HAVE_FUNCTION_ERROR_INJECTION
+ select FUNCTION_ERROR_INJECTION
+ help
+ Provide an admin-facing mechanism to make a chosen kernel function
+ return a fixed value without executing its body, as a temporary
+ mitigation for a security bug before a real fix is available.
+
+ Operators write "engage <symbol> <retval> [reason]" to
Should [reason] be shown at "engaged" ? I was expecting it, and in fact find it
very useful, but I don't see it.
# echo "engage __x64_sys_getuid 12 CVE-2026-99999-INCIDENT-4242" >
/sys/kernel/security/killswitch/control
# cat /sys/kernel/security/killswitch/engaged
__x64_sys_getuid retval=12 hits=12
This was a woopsie on my end: originally I planned to have a reason field, but
then decided to drop it to keep the patch simple. However, I forgot to fix up
the kconfig help text :(
If you think it'll be useful, I'm happy to add it back.
+#if IS_ENABLED(CONFIG_KUNIT)
+#include <kunit/test.h>
+
+/* Non-static so kallsyms resolves them without CONFIG_KALLSYMS_ALL. */
+int ks_kunit_target_int(int x);
+void *ks_kunit_target_ptr(int x);
+
+/* noipa keeps the call out-of-line and uneliminated. */
+__attribute__((__noipa__)) int ks_kunit_target_int(int x)
+{
+ return x + 1;
+}
+
+__attribute__((__noipa__)) void *ks_kunit_target_ptr(int x)
+{
+ return ERR_PTR(-EIO);
+}
When compiling with LLVM=1, I get the following error:
kernel/killswitch.c:708:16: error: unknown attribute '__noipa__' ignored
[-Werror,-Wunknown-attributes]
708 | __attribute__((__noipa__)) int ks_kunit_target_int(int x)
| ^~~~~~~~~
kernel/killswitch.c:713:16: error: unknown attribute '__noipa__' ignored
[-Werror,-Wunknown-attributes]
713 | __attribute__((__noipa__)) void *ks_kunit_target_ptr(int x)
| ^~~~~~~~~
Will fix, thanks!
--
Thanks,
Sasha
