security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++------ 1 file changed, 21 insertions(+), 6 deletions(-)
When both IMA and EVM fix modes are enabled, accessing a file with IMA
signature won't cause security.evm to be fixed. But this doesn't happen
to a file with correct IMA hash already set because accessing it will
cause setting security.ima again which triggers fixing security.evm
thanks to security_inode_post_setxattr->evm_update_evmxattr.
Let's use the same mechanism to fix security.evm for a file with IMA
signature.
Signed-off-by: Coiby Xu <coxu@redhat.com>
---
security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
index f435eff4667f..18c3907c5e44 100644
--- a/security/integrity/ima/ima_appraise.c
+++ b/security/integrity/ima/ima_appraise.c
@@ -595,12 +595,27 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
integrity_audit_msg(audit_msgno, inode, filename,
op, cause, rc, 0);
} else if (status != INTEGRITY_PASS) {
- /* Fix mode, but don't replace file signatures. */
- if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
- (!xattr_value ||
- xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
- if (!ima_fix_xattr(dentry, iint))
- status = INTEGRITY_PASS;
+ /*
+ * Fix mode, but don't replace file signatures.
+ *
+ * When EVM fix mode is also enabled, security.evm will be
+ * fixed automatically when security.ima is set because of
+ * security_inode_post_setxattr->evm_update_evmxattr.
+ */
+ if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig) {
+ if (!xattr_value ||
+ xattr_value->type != EVM_IMA_XATTR_DIGSIG) {
+ if (ima_fix_xattr(dentry, iint))
+ status = INTEGRITY_PASS;
+ } else if (xattr_value->type == EVM_IMA_XATTR_DIGSIG &&
+ evm_revalidate_status(XATTR_NAME_IMA)) {
+ if (!__vfs_setxattr_noperm(&nop_mnt_idmap,
+ dentry,
+ XATTR_NAME_IMA,
+ xattr_value,
+ xattr_len, 0))
+ status = INTEGRITY_PASS;
+ }
}
/*
base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
--
2.51.0On Tue, 2025-09-09 at 12:19 +0800, Coiby Xu wrote:
> When both IMA and EVM fix modes are enabled, accessing a file with IMA
> signature won't cause security.evm to be fixed. But this doesn't happen
> to a file with correct IMA hash already set because accessing it will
> cause setting security.ima again which triggers fixing security.evm
> thanks to security_inode_post_setxattr->evm_update_evmxattr.
>
> Let's use the same mechanism to fix security.evm for a file with IMA
> signature.
>
> Signed-off-by: Coiby Xu <coxu@redhat.com>
Agreed, re-writing the file signature stored as security.ima would force
security.evm to be updated.
Unfortunately, I'm missing something. ima_appraise_measurement() first verifies
the existing security.evm xattr, before verifying the security.ima xattr. If
the EVM HMAC fails to verify, it immediately exits ima_appraise_measurement().
security.ima in this case is never verified.
This patch seems to address the case where the existing security.evm is valid,
but the file signature stored in security.ima is invalid. (To get to the new
code, the "status" flag is not INTEGRITY_PASS.) Re-writing the same invalid
file signature would solve an invalid security.evm, but not an invalid IMA file
signature. What am I missing?
thanks,
Mimi
> ---
> security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++------
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> index f435eff4667f..18c3907c5e44 100644
> --- a/security/integrity/ima/ima_appraise.c
> +++ b/security/integrity/ima/ima_appraise.c
> @@ -595,12 +595,27 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
> integrity_audit_msg(audit_msgno, inode, filename,
> op, cause, rc, 0);
> } else if (status != INTEGRITY_PASS) {
> - /* Fix mode, but don't replace file signatures. */
> - if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
> - (!xattr_value ||
> - xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
> - if (!ima_fix_xattr(dentry, iint))
> - status = INTEGRITY_PASS;
> + /*
> + * Fix mode, but don't replace file signatures.
> + *
> + * When EVM fix mode is also enabled, security.evm will be
> + * fixed automatically when security.ima is set because of
> + * security_inode_post_setxattr->evm_update_evmxattr.
> + */
> + if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig) {
> + if (!xattr_value ||
> + xattr_value->type != EVM_IMA_XATTR_DIGSIG) {
> + if (ima_fix_xattr(dentry, iint))
> + status = INTEGRITY_PASS;
> + } else if (xattr_value->type == EVM_IMA_XATTR_DIGSIG &&
> + evm_revalidate_status(XATTR_NAME_IMA)) {
> + if (!__vfs_setxattr_noperm(&nop_mnt_idmap,
> + dentry,
> + XATTR_NAME_IMA,
> + xattr_value,
> + xattr_len, 0))
> + status = INTEGRITY_PASS;
> + }
> }
>
> /*
>
> base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
On Tue, Sep 09, 2025 at 11:31:20AM -0400, Mimi Zohar wrote:
>On Tue, 2025-09-09 at 12:19 +0800, Coiby Xu wrote:
>> When both IMA and EVM fix modes are enabled, accessing a file with IMA
>> signature won't cause security.evm to be fixed. But this doesn't happen
>> to a file with correct IMA hash already set because accessing it will
>> cause setting security.ima again which triggers fixing security.evm
>> thanks to security_inode_post_setxattr->evm_update_evmxattr.
>>
>> Let's use the same mechanism to fix security.evm for a file with IMA
>> signature.
>>
>> Signed-off-by: Coiby Xu <coxu@redhat.com>
>
>Agreed, re-writing the file signature stored as security.ima would force
>security.evm to be updated.
>
>Unfortunately, I'm missing something. ima_appraise_measurement() first verifies
>the existing security.evm xattr, before verifying the security.ima xattr. If
>the EVM HMAC fails to verify, it immediately exits ima_appraise_measurement().
>security.ima in this case is never verified.
>
>This patch seems to address the case where the existing security.evm is valid,
>but the file signature stored in security.ima is invalid. (To get to the new
>code, the "status" flag is not INTEGRITY_PASS.) Re-writing the same invalid
>file signature would solve an invalid security.evm, but not an invalid IMA file
>signature. What am I missing?
Hi, Mimi,
Thanks for raising the question! This patch is to address the case where
IMA signature is already added but security.evm doesn't yet exist. So
EVM HMAC fails to verify but there is no exiting
ima_appraise_measurement immediately.
And you are right that re-writing an invalid IMA file won't fix an
invalid IMA file signature. And even when IMA signature is valid, the
verification may fail because the key is missing from .ima keyring. This
happens because we need to turn off secure boot to enable fix mode. As a
result, CA keys won't be loaded into .machine keyring. Btw, if I'm not
mistaken, current IMA code assumes we are not supposed to fix IMA file
signature.
>
>thanks,
>
>Mimi
>
>> ---
>> security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++------
>> 1 file changed, 21 insertions(+), 6 deletions(-)
>>
>> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
>> index f435eff4667f..18c3907c5e44 100644
>> --- a/security/integrity/ima/ima_appraise.c
>> +++ b/security/integrity/ima/ima_appraise.c
>> @@ -595,12 +595,27 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
>> integrity_audit_msg(audit_msgno, inode, filename,
>> op, cause, rc, 0);
>> } else if (status != INTEGRITY_PASS) {
>> - /* Fix mode, but don't replace file signatures. */
>> - if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
>> - (!xattr_value ||
>> - xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
>> - if (!ima_fix_xattr(dentry, iint))
>> - status = INTEGRITY_PASS;
>> + /*
>> + * Fix mode, but don't replace file signatures.
>> + *
>> + * When EVM fix mode is also enabled, security.evm will be
>> + * fixed automatically when security.ima is set because of
>> + * security_inode_post_setxattr->evm_update_evmxattr.
>> + */
>> + if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig) {
>> + if (!xattr_value ||
>> + xattr_value->type != EVM_IMA_XATTR_DIGSIG) {
>> + if (ima_fix_xattr(dentry, iint))
>> + status = INTEGRITY_PASS;
>> + } else if (xattr_value->type == EVM_IMA_XATTR_DIGSIG &&
>> + evm_revalidate_status(XATTR_NAME_IMA)) {
>> + if (!__vfs_setxattr_noperm(&nop_mnt_idmap,
>> + dentry,
>> + XATTR_NAME_IMA,
>> + xattr_value,
>> + xattr_len, 0))
>> + status = INTEGRITY_PASS;
>> + }
>> }
>>
>> /*
>>
>> base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
>
--
Best regards,
Coiby
On Wed, 2025-09-10 at 09:20 +0800, Coiby Xu wrote:
> On Tue, Sep 09, 2025 at 11:31:20AM -0400, Mimi Zohar wrote:
> > On Tue, 2025-09-09 at 12:19 +0800, Coiby Xu wrote:
> > > When both IMA and EVM fix modes are enabled, accessing a file with IMA
> > > signature won't cause security.evm to be fixed. But this doesn't happen
> > > to a file with correct IMA hash already set because accessing it will
> > > cause setting security.ima again which triggers fixing security.evm
> > > thanks to security_inode_post_setxattr->evm_update_evmxattr.
> > >
> > > Let's use the same mechanism to fix security.evm for a file with IMA
> > > signature.
> > >
> > > Signed-off-by: Coiby Xu <coxu@redhat.com>
> >
> > Agreed, re-writing the file signature stored as security.ima would force
> > security.evm to be updated.
> >
> > Unfortunately, I'm missing something. ima_appraise_measurement() first verifies
> > the existing security.evm xattr, before verifying the security.ima xattr. If
> > the EVM HMAC fails to verify, it immediately exits ima_appraise_measurement().
> > security.ima in this case is never verified.
> >
> > This patch seems to address the case where the existing security.evm is valid,
> > but the file signature stored in security.ima is invalid. (To get to the new
> > code, the "status" flag is not INTEGRITY_PASS.) Re-writing the same invalid
> > file signature would solve an invalid security.evm, but not an invalid IMA file
> > signature. What am I missing?
>
> Hi, Mimi,
>
> Thanks for raising the question! This patch is to address the case where
> IMA signature is already added but security.evm doesn't yet exist. So
> EVM HMAC fails to verify but there is no exiting
> ima_appraise_measurement immediately.
>
> And you are right that re-writing an invalid IMA file won't fix an
> invalid IMA file signature. And even when IMA signature is valid, the
> verification may fail because the key is missing from .ima keyring. This
> happens because we need to turn off secure boot to enable fix mode. As a
> result, CA keys won't be loaded into .machine keyring. Btw, if I'm not
> mistaken, current IMA code assumes we are not supposed to fix IMA file
> signature.
> >
> > > ---
> > > security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++------
> > > 1 file changed, 21 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> > > index f435eff4667f..18c3907c5e44 100644
> > > --- a/security/integrity/ima/ima_appraise.c
> > > +++ b/security/integrity/ima/ima_appraise.c
> > > @@ -595,12 +595,27 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
> > > integrity_audit_msg(audit_msgno, inode, filename,
> > > op, cause, rc, 0);
> > > } else if (status != INTEGRITY_PASS) {
> > > - /* Fix mode, but don't replace file signatures. */
> > > - if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
> > > - (!xattr_value ||
> > > - xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
> > > - if (!ima_fix_xattr(dentry, iint))
> > > - status = INTEGRITY_PASS;
> > > + /*
> > > + * Fix mode, but don't replace file signatures.
> > > + *
> > > + * When EVM fix mode is also enabled, security.evm will be
> > > + * fixed automatically when security.ima is set because of
> > > + * security_inode_post_setxattr->evm_update_evmxattr.
> > > + */
> > > + if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig) {
> > > + if (!xattr_value ||
> > > + xattr_value->type != EVM_IMA_XATTR_DIGSIG) {
> > > + if (ima_fix_xattr(dentry, iint))
> > > + status = INTEGRITY_PASS;
> > > + } else if (xattr_value->type == EVM_IMA_XATTR_DIGSIG &&
> > > + evm_revalidate_status(XATTR_NAME_IMA)) {
> > > + if (!__vfs_setxattr_noperm(&nop_mnt_idmap,
> > > + dentry,
> > > + XATTR_NAME_IMA,
> > > + xattr_value,
> > > + xattr_len, 0))
> > > + status = INTEGRITY_PASS;
> > > + }
> > > }
Instead of re-writing the IMA signature without a clear explanation, define a
new EVM function named evm_fix_hmac() and add a call here in IMA. Only in EVM
fix mode would evm_fix_hmac() update the EVM hmac.
} else if (status != INTEGRITY_PASS) {
/*
* IMA fix mode updates the IMA file hash, which triggers EVM
* to update security.evm. ....
*
* Similarly, trigger fixing EVM HMAC for IMA file signatures.
*/
if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig) {
if (!xattr_value ||
xattr_value->type != EVM_IMA_XATTR_DIGSIG) {
if (ima_fix_xattr(dentry, iint))
status = INTEGRITY_PASS;
} else if (status == INTEGRITY_NOLABEL) {
evm_fix_hmac(dentry, XATTR_NAME_IMA, ....);
}
}
> > >
> > > /*
> > >
> > > base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
> >
>
On Mon, Sep 15, 2025 at 05:05:42PM -0400, Mimi Zohar wrote:
>On Wed, 2025-09-10 at 09:20 +0800, Coiby Xu wrote:
>> On Tue, Sep 09, 2025 at 11:31:20AM -0400, Mimi Zohar wrote:
>> > On Tue, 2025-09-09 at 12:19 +0800, Coiby Xu wrote:
>> > > When both IMA and EVM fix modes are enabled, accessing a file with IMA
>> > > signature won't cause security.evm to be fixed. But this doesn't happen
>> > > to a file with correct IMA hash already set because accessing it will
>> > > cause setting security.ima again which triggers fixing security.evm
>> > > thanks to security_inode_post_setxattr->evm_update_evmxattr.
>> > >
>> > > Let's use the same mechanism to fix security.evm for a file with IMA
>> > > signature.
>> > >
[...]
>> > > ---
>> > > security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++------
>> > > 1 file changed, 21 insertions(+), 6 deletions(-)
>> > >
>> > > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
>> > > index f435eff4667f..18c3907c5e44 100644
>> > > --- a/security/integrity/ima/ima_appraise.c
>> > > +++ b/security/integrity/ima/ima_appraise.c
>> > > @@ -595,12 +595,27 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
>> > > integrity_audit_msg(audit_msgno, inode, filename,
>> > > op, cause, rc, 0);
>> > > } else if (status != INTEGRITY_PASS) {
>> > > - /* Fix mode, but don't replace file signatures. */
>> > > - if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
>> > > - (!xattr_value ||
>> > > - xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
>> > > - if (!ima_fix_xattr(dentry, iint))
>> > > - status = INTEGRITY_PASS;
>> > > + /*
>> > > + * Fix mode, but don't replace file signatures.
>> > > + *
>> > > + * When EVM fix mode is also enabled, security.evm will be
>> > > + * fixed automatically when security.ima is set because of
>> > > + * security_inode_post_setxattr->evm_update_evmxattr.
>> > > + */
>> > > + if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig) {
>> > > + if (!xattr_value ||
>> > > + xattr_value->type != EVM_IMA_XATTR_DIGSIG) {
>> > > + if (ima_fix_xattr(dentry, iint))
>> > > + status = INTEGRITY_PASS;
>> > > + } else if (xattr_value->type == EVM_IMA_XATTR_DIGSIG &&
>> > > + evm_revalidate_status(XATTR_NAME_IMA)) {
>> > > + if (!__vfs_setxattr_noperm(&nop_mnt_idmap,
>> > > + dentry,
>> > > + XATTR_NAME_IMA,
>> > > + xattr_value,
>> > > + xattr_len, 0))
>> > > + status = INTEGRITY_PASS;
>> > > + }
>> > > }
>
>Instead of re-writing the IMA signature without a clear explanation, define a
>new EVM function named evm_fix_hmac() and add a call here in IMA. Only in EVM
>fix mode would evm_fix_hmac() update the EVM hmac.
>
> } else if (status != INTEGRITY_PASS) {
> /*
> * IMA fix mode updates the IMA file hash, which triggers EVM
> * to update security.evm. ....
> *
> * Similarly, trigger fixing EVM HMAC for IMA file signatures.
> */
> if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig) {
> if (!xattr_value ||
> xattr_value->type != EVM_IMA_XATTR_DIGSIG) {
> if (ima_fix_xattr(dentry, iint))
> status = INTEGRITY_PASS;
> } else if (status == INTEGRITY_NOLABEL) {
> evm_fix_hmac(dentry, XATTR_NAME_IMA, ....);
> }
> }
Thanks for the advice! I wonder if we should use existing
evm_update_evmxattr instead of defining a new EVM function.
/*
* Calculate the hmac and update security.evm xattr
*
* Expects to be called with i_mutex locked.
*/
int evm_update_evmxattr(struct dentry *dentry, const char *xattr_name,
const char *xattr_value, size_t xattr_value_len)
{
}
I already tried evm_update_evmxattr and can confirm it works. But later
I switched to __vfs_setxattr_noperm because I thought it's consistent
with current logic of adding security.evm when there is already correct
security.ima and it's a slightly smaller change.
--
Best regards,
Coiby
On Wed, 2025-09-10 at 09:20 +0800, Coiby Xu wrote:
> On Tue, Sep 09, 2025 at 11:31:20AM -0400, Mimi Zohar wrote:
> > On Tue, 2025-09-09 at 12:19 +0800, Coiby Xu wrote:
> > > When both IMA and EVM fix modes are enabled, accessing a file with IMA
> > > signature won't cause security.evm to be fixed. But this doesn't happen
> > > to a file with correct IMA hash already set because accessing it will
> > > cause setting security.ima again which triggers fixing security.evm
> > > thanks to security_inode_post_setxattr->evm_update_evmxattr.
> > >
> > > Let's use the same mechanism to fix security.evm for a file with IMA
> > > signature.
> > >
> > > Signed-off-by: Coiby Xu <coxu@redhat.com>
> >
> > Agreed, re-writing the file signature stored as security.ima would force
> > security.evm to be updated.
> >
> > Unfortunately, I'm missing something. ima_appraise_measurement() first verifies
> > the existing security.evm xattr, before verifying the security.ima xattr. If
> > the EVM HMAC fails to verify, it immediately exits ima_appraise_measurement().
> > security.ima in this case is never verified.
> >
> > This patch seems to address the case where the existing security.evm is valid,
> > but the file signature stored in security.ima is invalid. (To get to the new
> > code, the "status" flag is not INTEGRITY_PASS.) Re-writing the same invalid
> > file signature would solve an invalid security.evm, but not an invalid IMA file
> > signature. What am I missing?
>
> Hi, Mimi,
>
> Thanks for raising the question! This patch is to address the case where
> IMA signature is already added but security.evm doesn't yet exist. So
> EVM HMAC fails to verify but there is no exiting
> ima_appraise_measurement immediately.
>
> And you are right that re-writing an invalid IMA file won't fix an
> invalid IMA file signature. And even when IMA signature is valid, the
> verification may fail because the key is missing from .ima keyring. This
> happens because we need to turn off secure boot to enable fix mode. As a
> result, CA keys won't be loaded into .machine keyring.
> Btw, if I'm not
> mistaken, current IMA code assumes we are not supposed to fix IMA file
> signature.
Right, unlike file hashes, new or the same file signature can be written, but
cannot be "fixed" in the literal sense, as that would require calculating the
file hash and signing it with a private key.
This patch triggers "fixing" the EVM HMAC by re-writing the existing IMA file
signature. I assume the same result could be achieved by simply re-installing
the file signature. In both cases, the EVM HMAC key needs to exist and be
loaded.
>
> >
> > > ---
> > > security/integrity/ima/ima_appraise.c | 27 +++++++++++++++++++++------
> > > 1 file changed, 21 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
> > > index f435eff4667f..18c3907c5e44 100644
> > > --- a/security/integrity/ima/ima_appraise.c
> > > +++ b/security/integrity/ima/ima_appraise.c
> > > @@ -595,12 +595,27 @@ int ima_appraise_measurement(enum ima_hooks func, struct ima_iint_cache *iint,
> > > integrity_audit_msg(audit_msgno, inode, filename,
> > > op, cause, rc, 0);
> > > } else if (status != INTEGRITY_PASS) {
> > > - /* Fix mode, but don't replace file signatures. */
> > > - if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig &&
> > > - (!xattr_value ||
> > > - xattr_value->type != EVM_IMA_XATTR_DIGSIG)) {
> > > - if (!ima_fix_xattr(dentry, iint))
> > > - status = INTEGRITY_PASS;
> > > + /*
> > > + * Fix mode, but don't replace file signatures.
> > > + *
> > > + * When EVM fix mode is also enabled, security.evm will be
> > > + * fixed automatically when security.ima is set because of
> > > + * security_inode_post_setxattr->evm_update_evmxattr.
> > > + */
> > > + if ((ima_appraise & IMA_APPRAISE_FIX) && !try_modsig) {
> > > + if (!xattr_value ||
> > > + xattr_value->type != EVM_IMA_XATTR_DIGSIG) {
> > > + if (ima_fix_xattr(dentry, iint))
> > > + status = INTEGRITY_PASS;
> > > + } else if (xattr_value->type == EVM_IMA_XATTR_DIGSIG &&
> > > + evm_revalidate_status(XATTR_NAME_IMA)) {
> > > + if (!__vfs_setxattr_noperm(&nop_mnt_idmap,
> > > + dentry,
> > > + XATTR_NAME_IMA,
> > > + xattr_value,
> > > + xattr_len, 0))
> > > + status = INTEGRITY_PASS;
> > > + }
> > > }
> > >
> > > /*
> > >
> > > base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
> >
>
On Wed, Sep 10, 2025 at 07:15:19AM -0400, Mimi Zohar wrote: >On Wed, 2025-09-10 at 09:20 +0800, Coiby Xu wrote: >> On Tue, Sep 09, 2025 at 11:31:20AM -0400, Mimi Zohar wrote: >> > On Tue, 2025-09-09 at 12:19 +0800, Coiby Xu wrote: >> > > When both IMA and EVM fix modes are enabled, accessing a file with IMA >> > > signature won't cause security.evm to be fixed. But this doesn't happen >> > > to a file with correct IMA hash already set because accessing it will >> > > cause setting security.ima again which triggers fixing security.evm >> > > thanks to security_inode_post_setxattr->evm_update_evmxattr. >> > > >> > > Let's use the same mechanism to fix security.evm for a file with IMA >> > > signature. >> > > >> > > Signed-off-by: Coiby Xu <coxu@redhat.com> >> > >> > Agreed, re-writing the file signature stored as security.ima would force >> > security.evm to be updated. >> > >> > Unfortunately, I'm missing something. ima_appraise_measurement() first verifies >> > the existing security.evm xattr, before verifying the security.ima xattr. If >> > the EVM HMAC fails to verify, it immediately exits ima_appraise_measurement(). >> > security.ima in this case is never verified. >> > >> > This patch seems to address the case where the existing security.evm is valid, >> > but the file signature stored in security.ima is invalid. (To get to the new >> > code, the "status" flag is not INTEGRITY_PASS.) Re-writing the same invalid >> > file signature would solve an invalid security.evm, but not an invalid IMA file >> > signature. What am I missing? >> >> Hi, Mimi, >> >> Thanks for raising the question! This patch is to address the case where >> IMA signature is already added but security.evm doesn't yet exist. So >> EVM HMAC fails to verify but there is no exiting >> ima_appraise_measurement immediately. >> >> And you are right that re-writing an invalid IMA file won't fix an >> invalid IMA file signature. And even when IMA signature is valid, the >> verification may fail because the key is missing from .ima keyring. This >> happens because we need to turn off secure boot to enable fix mode. As a >> result, CA keys won't be loaded into .machine keyring. > >> Btw, if I'm not >> mistaken, current IMA code assumes we are not supposed to fix IMA file >> signature. > >Right, unlike file hashes, new or the same file signature can be written, but >cannot be "fixed" in the literal sense, as that would require calculating the >file hash and signing it with a private key. Thanks for the confirmation! I also added some code comments to explain the IMA iint cache atomic_flags including IMA_DIGSIG in v2. > >This patch triggers "fixing" the EVM HMAC by re-writing the existing IMA file >signature. I assume the same result could be achieved by simply re-installing >the file signature. In both cases, the EVM HMAC key needs to exist and be >loaded. -- Best regards, Coiby
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