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Date: Wed, 7 Aug 2019 17:06:58 -0700 From: Matthew Garrett <matthewgarrett@...gle.com> To: jmorris@...ei.org Cc: linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org, linux-api@...r.kernel.org, Matthew Garrett <mjg59@...f.ucam.org>, David Howells <dhowells@...hat.com>, Matthew Garrett <mjg59@...gle.com>, Dave Young <dyoung@...hat.com>, Kees Cook <keescook@...omium.org>, kexec@...ts.infradead.org Subject: [PATCH V38 06/29] kexec_load: Disable at runtime if the kernel is locked down From: Matthew Garrett <mjg59@...f.ucam.org> The kexec_load() syscall permits the loading and execution of arbitrary code in ring 0, which is something that lock-down is meant to prevent. It makes sense to disable kexec_load() in this situation. This does not affect kexec_file_load() syscall which can check for a signature on the image to be booted. Signed-off-by: David Howells <dhowells@...hat.com> Signed-off-by: Matthew Garrett <mjg59@...gle.com> Acked-by: Dave Young <dyoung@...hat.com> Reviewed-by: Kees Cook <keescook@...omium.org> cc: kexec@...ts.infradead.org --- include/linux/security.h | 1 + kernel/kexec.c | 8 ++++++++ security/lockdown/lockdown.c | 1 + 3 files changed, 10 insertions(+) diff --git a/include/linux/security.h b/include/linux/security.h index 9458152601b5..69c5de539e9a 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -105,6 +105,7 @@ enum lockdown_reason { LOCKDOWN_NONE, LOCKDOWN_MODULE_SIGNATURE, LOCKDOWN_DEV_MEM, + LOCKDOWN_KEXEC, LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_CONFIDENTIALITY_MAX, }; diff --git a/kernel/kexec.c b/kernel/kexec.c index 1b018f1a6e0d..bc933c0db9bf 100644 --- a/kernel/kexec.c +++ b/kernel/kexec.c @@ -205,6 +205,14 @@ static inline int kexec_load_check(unsigned long nr_segments, if (result < 0) return result; + /* + * kexec can be used to circumvent module loading restrictions, so + * prevent loading in that case + */ + result = security_locked_down(LOCKDOWN_KEXEC); + if (result) + return result; + /* * Verify we have a legal set of flags * This leaves us room for future extensions. diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c index d2ef29d9f0b2..6f302c156bc8 100644 --- a/security/lockdown/lockdown.c +++ b/security/lockdown/lockdown.c @@ -20,6 +20,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_NONE] = "none", [LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading", [LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port", + [LOCKDOWN_KEXEC] = "kexec of unsigned images", [LOCKDOWN_INTEGRITY_MAX] = "integrity", [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", }; -- 2.22.0.770.g0f2c4a37fd-goog
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