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
> +#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)
| ^~~~~~~~~
Thanks,
--breno
