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EVM: Allow userspace to signal an RSA key has been loaded

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EVM will only perform validation once a key has been loaded. This key
may either be a symmetric trusted key (for HMAC validation and creation)
or the public half of an asymmetric key (for digital signature
validation). The /sys/kernel/security/evm interface allows userland to
signal that a symmetric key has been loaded, but does not allow userland
to signal that an asymmetric public key has been loaded.

This patch extends the interface to permit userspace to pass a bitmask
of loaded key types. It also allows userspace to block loading of a
symmetric key in order to avoid a compromised system from being able to
load an additional key type later.

Signed-off-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
This commit is contained in:
Matthew Garrett
2017-10-11 12:10:14 -07:00
committed by Mimi Zohar
parent 096b854648
commit f00d797507
3 changed files with 54 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files
security/integrity/evm/evm.h
+3
View File
@@ -23,6 +23,9 @@
#define EVM_INIT_HMAC 0x0001
#define EVM_INIT_X509 0x0002
#define EVM_SETUP 0x80000000 /* userland has signaled key load */
#define EVM_INIT_MASK (EVM_INIT_HMAC | EVM_INIT_X509 | EVM_SETUP)
extern int evm_initialized;
extern char *evm_hmac;
security/integrity/evm/evm_secfs.c
+18 -13
View File
@@ -40,7 +40,7 @@ static ssize_t evm_read_key(struct file *filp, char __user *buf,
if (*ppos != 0)
return 0;
sprintf(temp, "%d", evm_initialized);
sprintf(temp, "%d", (evm_initialized & ~EVM_SETUP));
rc = simple_read_from_buffer(buf, count, ppos, temp, strlen(temp));
return rc;
@@ -61,24 +61,29 @@ static ssize_t evm_read_key(struct file *filp, char __user *buf,
static ssize_t evm_write_key(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
char temp[80];
int i;
int i, ret;
if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_INIT_HMAC))
if (!capable(CAP_SYS_ADMIN) || (evm_initialized & EVM_SETUP))
return -EPERM;
if (count >= sizeof(temp) || count == 0)
ret = kstrtoint_from_user(buf, count, 0, &i);
if (ret)
return ret;
/* Reject invalid values */
if (!i || (i & ~EVM_INIT_MASK) != 0)
return -EINVAL;
if (copy_from_user(temp, buf, count) != 0)
return -EFAULT;
if (i & EVM_INIT_HMAC) {
ret = evm_init_key();
if (ret != 0)
return ret;
/* Forbid further writes after the symmetric key is loaded */
i |= EVM_SETUP;
}
temp[count] = '\0';
if ((sscanf(temp, "%d", &i) != 1) || (i != 1))
return -EINVAL;
evm_init_key();
evm_initialized |= i;
return count;
}