From: Matthew Garrett <matthewgarrett@google.com>
To: jmorris@namei.org
Cc: linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
Matthew Garrett <matthewgarrett@google.com>,
Matthew Garrett <mjg59@google.com>,
Mimi Zohar <zohar@linux.ibm.com>,
Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
linux-integrity@vger.kernel.org
Subject: [PATCH V36 25/29] kexec: Allow kexec_file() with appropriate IMA policy when locked down
Date: Thu, 18 Jul 2019 12:44:11 -0700 [thread overview]
Message-ID: <20190718194415.108476-26-matthewgarrett@google.com> (raw)
In-Reply-To: <20190718194415.108476-1-matthewgarrett@google.com>
Systems in lockdown mode should block the kexec of untrusted kernels.
For x86 and ARM we can ensure that a kernel is trustworthy by validating
a PE signature, but this isn't possible on other architectures. On those
platforms we can use IMA digital signatures instead. Add a function to
determine whether IMA has or will verify signatures for a given event type,
and if so permit kexec_file() even if the kernel is otherwise locked down.
This is restricted to cases where CONFIG_INTEGRITY_TRUSTED_KEYRING is set
in order to prevent an attacker from loading additional keys at runtime.
Signed-off-by: Matthew Garrett <mjg59@google.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Cc: Dmitry Kasatkin <dmitry.kasatkin@gmail.com>
Cc: linux-integrity@vger.kernel.org
---
include/linux/ima.h | 9 ++++++
kernel/kexec_file.c | 12 +++++--
security/integrity/ima/ima.h | 2 ++
security/integrity/ima/ima_main.c | 2 +-
security/integrity/ima/ima_policy.c | 50 +++++++++++++++++++++++++++++
5 files changed, 72 insertions(+), 3 deletions(-)
diff --git a/include/linux/ima.h b/include/linux/ima.h
index a20ad398d260..1c37f17f7203 100644
--- a/include/linux/ima.h
+++ b/include/linux/ima.h
@@ -131,4 +131,13 @@ static inline int ima_inode_removexattr(struct dentry *dentry,
return 0;
}
#endif /* CONFIG_IMA_APPRAISE */
+
+#if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)
+extern bool ima_appraise_signature(enum kernel_read_file_id func);
+#else
+static inline bool ima_appraise_signature(enum kernel_read_file_id func)
+{
+ return false;
+}
+#endif /* CONFIG_IMA_APPRAISE && CONFIG_INTEGRITY_TRUSTED_KEYRING */
#endif /* _LINUX_IMA_H */
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index dd06f1070d66..13c9960a5860 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -228,9 +228,17 @@ kimage_file_prepare_segments(struct kimage *image, int kernel_fd, int initrd_fd,
goto out;
}
- ret = security_locked_down(LOCKDOWN_KEXEC);
- if (ret)
+ ret = 0;
+
+ /* If IMA is guaranteed to appraise a signature on the kexec
+ * image, permit it even if the kernel is otherwise locked
+ * down.
+ */
+ if (!ima_appraise_signature(READING_KEXEC_IMAGE) &&
+ security_locked_down(LOCKDOWN_KEXEC)) {
+ ret = -EPERM;
goto out;
+ }
break;
diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
index 011b91c79351..64dcb11cf444 100644
--- a/security/integrity/ima/ima.h
+++ b/security/integrity/ima/ima.h
@@ -113,6 +113,8 @@ struct ima_kexec_hdr {
u64 count;
};
+extern const int read_idmap[];
+
#ifdef CONFIG_HAVE_IMA_KEXEC
void ima_load_kexec_buffer(void);
#else
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index 584019728660..b9f57503af2c 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -502,7 +502,7 @@ int ima_read_file(struct file *file, enum kernel_read_file_id read_id)
return 0;
}
-static const int read_idmap[READING_MAX_ID] = {
+const int read_idmap[READING_MAX_ID] = {
[READING_FIRMWARE] = FIRMWARE_CHECK,
[READING_FIRMWARE_PREALLOC_BUFFER] = FIRMWARE_CHECK,
[READING_MODULE] = MODULE_CHECK,
diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 6df7f641ff66..827f1e33fe86 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -1456,3 +1456,53 @@ int ima_policy_show(struct seq_file *m, void *v)
return 0;
}
#endif /* CONFIG_IMA_READ_POLICY */
+
+#if defined(CONFIG_IMA_APPRAISE) && defined(CONFIG_INTEGRITY_TRUSTED_KEYRING)
+/*
+ * ima_appraise_signature: whether IMA will appraise a given function using
+ * an IMA digital signature. This is restricted to cases where the kernel
+ * has a set of built-in trusted keys in order to avoid an attacker simply
+ * loading additional keys.
+ */
+bool ima_appraise_signature(enum kernel_read_file_id id)
+{
+ struct ima_rule_entry *entry;
+ bool found = false;
+ enum ima_hooks func;
+
+ if (id >= READING_MAX_ID)
+ return false;
+
+ func = read_idmap[id] ?: FILE_CHECK;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(entry, ima_rules, list) {
+ if (entry->action != APPRAISE)
+ continue;
+
+ /*
+ * A generic entry will match, but otherwise require that it
+ * match the func we're looking for
+ */
+ if (entry->func && entry->func != func)
+ continue;
+
+ /*
+ * We require this to be a digital signature, not a raw IMA
+ * hash.
+ */
+ if (entry->flags & IMA_DIGSIG_REQUIRED)
+ found = true;
+
+ /*
+ * We've found a rule that matches, so break now even if it
+ * didn't require a digital signature - a later rule that does
+ * won't override it, so would be a false positive.
+ */
+ break;
+ }
+
+ rcu_read_unlock();
+ return found;
+}
+#endif /* CONFIG_IMA_APPRAISE && CONFIG_INTEGRITY_TRUSTED_KEYRING */
--
2.22.0.510.g264f2c817a-goog
next prev parent reply other threads:[~2019-07-18 19:45 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-18 19:43 [PATCH V36 00/29] security: Add kernel lockdown functionality Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 01/29] security: Support early LSMs Matthew Garrett
2019-07-18 20:02 ` Casey Schaufler
2019-07-18 19:43 ` [PATCH V36 02/29] security: Add a "locked down" LSM hook Matthew Garrett
2019-07-18 20:03 ` Casey Schaufler
2019-07-18 19:43 ` [PATCH V36 03/29] security: Add a static lockdown policy LSM Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 04/29] Enforce module signatures if the kernel is locked down Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 05/29] Restrict /dev/{mem,kmem,port} when " Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 06/29] kexec_load: Disable at runtime if " Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 07/29] Copy secure_boot flag in boot params across kexec reboot Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 08/29] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 09/29] kexec_file: Restrict at runtime if the kernel is locked down Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 10/29] hibernate: Disable when " Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 11/29] PCI: Lock down BAR access " Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 12/29] x86: Lock down IO port " Matthew Garrett
2019-07-18 19:43 ` [PATCH V36 13/29] x86/msr: Restrict MSR " Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 14/29] ACPI: Limit access to custom_method " Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 15/29] acpi: Ignore acpi_rsdp kernel param when the kernel has been " Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 16/29] acpi: Disable ACPI table override if the kernel is " Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 17/29] Prohibit PCMCIA CIS storage when " Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 18/29] Lock down TIOCSSERIAL Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 19/29] Lock down module params that specify hardware parameters (eg. ioport) Matthew Garrett
2019-07-29 21:47 ` Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 20/29] x86/mmiotrace: Lock down the testmmiotrace module Matthew Garrett
2019-07-18 21:06 ` Kees Cook
2019-07-18 19:44 ` [PATCH V36 21/29] Lock down /proc/kcore Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 22/29] Lock down tracing and perf kprobes when in confidentiality mode Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 23/29] bpf: Restrict bpf when kernel lockdown is " Matthew Garrett
2019-07-18 21:06 ` Kees Cook
2019-07-29 21:47 ` Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 24/29] Lock down perf when " Matthew Garrett
2019-07-18 19:44 ` Matthew Garrett [this message]
2019-07-18 19:44 ` [PATCH V36 26/29] debugfs: Restrict debugfs when the kernel is locked down Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 27/29] tracefs: Restrict tracefs " Matthew Garrett
2019-07-25 2:23 ` Steven Rostedt
2019-07-30 18:47 ` [PATCH] " Matthew Garrett
2019-07-31 1:48 ` Steven Rostedt
2019-07-18 19:44 ` [PATCH V36 28/29] efi: Restrict efivar_ssdt_load " Matthew Garrett
2019-07-18 19:44 ` [PATCH V36 29/29] lockdown: Print current->comm in restriction messages Matthew Garrett
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