From: Roberto Sassu roberto.sassu@huawei.com
euleros inclusion category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I7QZ2M CVE: NA
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IMA and EVM have been designed as two independent subsystems: the first for checking the integrity of file data; the second for checking file metadata. Making them independent allows users to adopt them incrementally.
The point of intersection is in IMA-Appraise, which calls evm_verifyxattr() to ensure that security.ima wasn't modified during an offline attack. The design choice, to ensure incremental adoption, was to continue appraisal verification if evm_verifyxattr() returns INTEGRITY_UNKNOWN. This value is returned when EVM is not enabled in the kernel configuration, or if the HMAC key has not been loaded yet.
Although this choice appears legitimate, it might not be suitable for hardened systems, where the administrator expects that access is denied if there is any error. An attacker could intentionally delete the EVM keys from the system and set the file digest in security.ima to the actual file digest so that the final appraisal status is INTEGRITY_PASS.
This patch allows such hardened systems to strictly enforce an access control policy based on the validity of signatures/HMACs, by introducing two new values for the ima_appraise= kernel option: enforce-evm and log-evm.
Cc: stable@vger.kernel.org Fixes: 2fe5d6def1672 ("ima: integrity appraisal extension") Signed-off-by: Roberto Sassu roberto.sassu@huawei.com Signed-off-by: Tianxing Zhang zhangtianxing3@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com Signed-off-by: zhoushuiqing zhoushuiqing2@huawei.com --- Documentation/admin-guide/kernel-parameters.txt | 3 ++- security/integrity/ima/ima_appraise.c | 9 +++++++++ 2 files changed, 11 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 9e5bab29685f..ee50a3b91d73 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1941,7 +1941,8 @@ Set number of hash buckets for inode cache.
ima_appraise= [IMA] appraise integrity measurements - Format: { "off" | "enforce" | "fix" | "log" } + Format: { "off" | "enforce" | "fix" | "log" | + "enforce-evm" | "log-evm" } default: "enforce"
ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c index 491c1aca0b1c..08ae5d7faa1d 100644 --- a/security/integrity/ima/ima_appraise.c +++ b/security/integrity/ima/ima_appraise.c @@ -19,6 +19,7 @@
#include "ima.h"
+static bool ima_appraise_req_evm __ro_after_init; #ifdef CONFIG_IMA_APPRAISE_BOOTPARAM static char *ima_appraise_cmdline_default __initdata; core_param(ima_appraise, ima_appraise_cmdline_default, charp, 0); @@ -52,6 +53,10 @@ void __init ima_appraise_parse_cmdline(void) } else { ima_appraise = appraisal_state; } + + if (strcmp(str, "enforce-evm") == 0 || + strcmp(str, "log-evm") == 0) + ima_appraise_req_evm = true; } #endif
@@ -522,7 +527,11 @@ int ima_appraise_measurement(enum ima_hooks func, switch (status) { case INTEGRITY_PASS: case INTEGRITY_PASS_IMMUTABLE: + break; case INTEGRITY_UNKNOWN: + if (ima_appraise_req_evm && + xattr_value->type != EVM_IMA_XATTR_DIGSIG) + goto out; break; case INTEGRITY_NOXATTRS: /* No EVM protected xattrs. */ /* It's fine not to have xattrs when using a modsig. */