[PATCH 0/1] crypto: ccp: use file mode for sev ioctl permissions

[PATCH 0/1] crypto: ccp: use file mode for sev ioctl permissions

[Connor Kuehl]

Some background:

My team is working on a project that interacts very closely with
SEV so we have a layer of code that wraps around the SEV ioctl calls.
We have an automated test suite that ends up testing these ioctls
on our test machine.

We are in the process of adding this test machine as a dedicated test
runner in our continuous integration process. Any time someone opens a
pull request against our project, this test runner automatically checks
that code out and executes the tests.

Right now, the SEV ioctls that affect the state of the platform require
CAP_SYS_ADMIN to run. This is not a capability we can give to an
automated test runner, because it means that anyone who would like to
contribute to the project would be able to run any code they want (for
good or evil) as CAP_SYS_ADMIN on our machine.

This patch replaces the check for CAP_SYS_ADMIN with a check that can
still be easily controlled by an administrator with the file permissions
ACL. This way access to the device can still be controlled, but without
also assigning such broad system privileges at the same time.

Connor Kuehl (1):
  crypto: ccp: use file mode for sev ioctl permissions

 drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

-- 
2.24.1

[PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[Connor Kuehl]

Instead of using CAP_SYS_ADMIN which is restricted to the root user,
check the file mode for write permissions before executing commands that
can affect the platform. This allows for more fine-grained access
control to the SEV ioctl interface. This would allow a SEV-only user
or group the ability to administer the platform without requiring them
to be root or granting them overly powerful permissions.

For example:

chown root:root /dev/sev
chmod 600 /dev/sev
setfacl -m g:sev:r /dev/sev
setfacl -m g:sev-admin:rw /dev/sev

In this instance, members of the "sev-admin" group have the ability to
perform all ioctl calls (including the ones that modify platform state).
Members of the "sev" group only have access to the ioctls that do not
modify the platform state.

This also makes opening "/dev/sev" more consistent with how file
descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
the file descriptor could be opened read-only but could still execute
ioctls that modify the platform state. This patch enforces that the file
descriptor is opened with write privileges if it is going to be used to
modify the platform state.

This flexibility is completely opt-in, and if it is not desirable by
the administrator then they do not need to give anyone else access to
/dev/sev.

Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
---
 drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index e467860f797d..416b80938a3e 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -283,11 +283,11 @@ static int sev_get_platform_state(int *state, int *error)
 	return rc;
 }
 
-static int sev_ioctl_do_reset(struct sev_issue_cmd *argp)
+static int sev_ioctl_do_reset(struct sev_issue_cmd *argp, bool writable)
 {
 	int state, rc;
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (!writable)
 		return -EPERM;
 
 	/*
@@ -331,12 +331,12 @@ static int sev_ioctl_do_platform_status(struct sev_issue_cmd *argp)
 	return ret;
 }
 
-static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
+static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp, bool writable)
 {
 	struct sev_device *sev = psp_master->sev_data;
 	int rc;
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (!writable)
 		return -EPERM;
 
 	if (sev->state == SEV_STATE_UNINIT) {
@@ -348,7 +348,7 @@ static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
 	return __sev_do_cmd_locked(cmd, NULL, &argp->error);
 }
 
-static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
+static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp, bool writable)
 {
 	struct sev_device *sev = psp_master->sev_data;
 	struct sev_user_data_pek_csr input;
@@ -356,7 +356,7 @@ static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
 	void *blob = NULL;
 	int ret;
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (!writable)
 		return -EPERM;
 
 	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
@@ -539,7 +539,7 @@ static int sev_update_firmware(struct device *dev)
 	return ret;
 }
 
-static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
+static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp, bool writable)
 {
 	struct sev_device *sev = psp_master->sev_data;
 	struct sev_user_data_pek_cert_import input;
@@ -547,7 +547,7 @@ static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
 	void *pek_blob, *oca_blob;
 	int ret;
 
-	if (!capable(CAP_SYS_ADMIN))
+	if (!writable)
 		return -EPERM;
 
 	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
@@ -698,7 +698,7 @@ static int sev_ioctl_do_get_id(struct sev_issue_cmd *argp)
 	return ret;
 }
 
-static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
+static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp, bool writable)
 {
 	struct sev_device *sev = psp_master->sev_data;
 	struct sev_user_data_pdh_cert_export input;
@@ -708,7 +708,7 @@ static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
 
 	/* If platform is not in INIT state then transition it to INIT. */
 	if (sev->state != SEV_STATE_INIT) {
-		if (!capable(CAP_SYS_ADMIN))
+		if (!writable)
 			return -EPERM;
 
 		ret = __sev_platform_init_locked(&argp->error);
@@ -801,6 +801,7 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
 	void __user *argp = (void __user *)arg;
 	struct sev_issue_cmd input;
 	int ret = -EFAULT;
+	bool writable = file->f_mode & FMODE_WRITE;
 
 	if (!psp_master || !psp_master->sev_data)
 		return -ENODEV;
@@ -819,25 +820,25 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
 	switch (input.cmd) {
 
 	case SEV_FACTORY_RESET:
-		ret = sev_ioctl_do_reset(&input);
+		ret = sev_ioctl_do_reset(&input, writable);
 		break;
 	case SEV_PLATFORM_STATUS:
 		ret = sev_ioctl_do_platform_status(&input);
 		break;
 	case SEV_PEK_GEN:
-		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input);
+		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input, writable);
 		break;
 	case SEV_PDH_GEN:
-		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input);
+		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input, writable);
 		break;
 	case SEV_PEK_CSR:
-		ret = sev_ioctl_do_pek_csr(&input);
+		ret = sev_ioctl_do_pek_csr(&input, writable);
 		break;
 	case SEV_PEK_CERT_IMPORT:
-		ret = sev_ioctl_do_pek_import(&input);
+		ret = sev_ioctl_do_pek_import(&input, writable);
 		break;
 	case SEV_PDH_CERT_EXPORT:
-		ret = sev_ioctl_do_pdh_export(&input);
+		ret = sev_ioctl_do_pdh_export(&input, writable);
 		break;
 	case SEV_GET_ID:
 		pr_warn_once("SEV_GET_ID command is deprecated, use SEV_GET_ID2\n");
-- 
2.24.1

Re: [PATCH 0/1] crypto: ccp: use file mode for sev ioctl permissions

[Nathaniel McCallum]

On Fri, Mar 6, 2020 at 12:20 PM Connor Kuehl <ckuehl@redhat.com> wrote:
>
> Some background:
>
> My team is working on a project that interacts very closely with
> SEV so we have a layer of code that wraps around the SEV ioctl calls.
> We have an automated test suite that ends up testing these ioctls
> on our test machine.
>
> We are in the process of adding this test machine as a dedicated test
> runner in our continuous integration process. Any time someone opens a
> pull request against our project, this test runner automatically checks
> that code out and executes the tests.
>
> Right now, the SEV ioctls that affect the state of the platform require
> CAP_SYS_ADMIN to run. This is not a capability we can give to an
> automated test runner, because it means that anyone who would like to
> contribute to the project would be able to run any code they want (for
> good or evil) as CAP_SYS_ADMIN on our machine.
>
> This patch replaces the check for CAP_SYS_ADMIN with a check that can
> still be easily controlled by an administrator with the file permissions
> ACL. This way access to the device can still be controlled, but without
> also assigning such broad system privileges at the same time.
>
> Connor Kuehl (1):
>   crypto: ccp: use file mode for sev ioctl permissions
>
>  drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
>
> --
> 2.24.1
>

One additional note is that this permission structure is more flexible
for general SEV usage anyway, and isn't special-case for our usage.
Currently, the SEV admin commands are mostly limited to public key
certificate management. I would imagine that it would be desirable to
have a sev-admin account which can automate the certificate management
without having CAP_SYS_ADMIN for the rest of the system. So we believe
this patch has broader applicability than just our corner case.

Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[David Rientjes]

On Fri, 6 Mar 2020, Connor Kuehl wrote:

> Instead of using CAP_SYS_ADMIN which is restricted to the root user,
> check the file mode for write permissions before executing commands that
> can affect the platform. This allows for more fine-grained access
> control to the SEV ioctl interface. This would allow a SEV-only user
> or group the ability to administer the platform without requiring them
> to be root or granting them overly powerful permissions.
> 
> For example:
> 
> chown root:root /dev/sev
> chmod 600 /dev/sev

Hi Connor,

I'm curious why do you need to do the two above commands?  It implies that 
/dev/sev is either not owned by root or that it is not already restricted 
to only being owner read and writable.

Or perhaps these two commands were included only for clarity to explain 
what the defaults should be?

> setfacl -m g:sev:r /dev/sev
> setfacl -m g:sev-admin:rw /dev/sev
> 
> In this instance, members of the "sev-admin" group have the ability to
> perform all ioctl calls (including the ones that modify platform state).
> Members of the "sev" group only have access to the ioctls that do not
> modify the platform state.
> 
> This also makes opening "/dev/sev" more consistent with how file
> descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
> the file descriptor could be opened read-only but could still execute
> ioctls that modify the platform state. This patch enforces that the file
> descriptor is opened with write privileges if it is going to be used to
> modify the platform state.
> 
> This flexibility is completely opt-in, and if it is not desirable by
> the administrator then they do not need to give anyone else access to
> /dev/sev.
> 
> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> ---
>  drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index e467860f797d..416b80938a3e 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -283,11 +283,11 @@ static int sev_get_platform_state(int *state, int *error)
>  	return rc;
>  }
>  
> -static int sev_ioctl_do_reset(struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_reset(struct sev_issue_cmd *argp, bool writable)
>  {
>  	int state, rc;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!writable)
>  		return -EPERM;
>  
>  	/*
> @@ -331,12 +331,12 @@ static int sev_ioctl_do_platform_status(struct sev_issue_cmd *argp)
>  	return ret;
>  }
>  
> -static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp, bool writable)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	int rc;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!writable)
>  		return -EPERM;
>  
>  	if (sev->state == SEV_STATE_UNINIT) {
> @@ -348,7 +348,7 @@ static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
>  	return __sev_do_cmd_locked(cmd, NULL, &argp->error);
>  }
>  
> -static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp, bool writable)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	struct sev_user_data_pek_csr input;
> @@ -356,7 +356,7 @@ static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
>  	void *blob = NULL;
>  	int ret;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!writable)
>  		return -EPERM;
>  
>  	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> @@ -539,7 +539,7 @@ static int sev_update_firmware(struct device *dev)
>  	return ret;
>  }
>  
> -static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp, bool writable)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	struct sev_user_data_pek_cert_import input;
> @@ -547,7 +547,7 @@ static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
>  	void *pek_blob, *oca_blob;
>  	int ret;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!writable)
>  		return -EPERM;
>  
>  	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> @@ -698,7 +698,7 @@ static int sev_ioctl_do_get_id(struct sev_issue_cmd *argp)
>  	return ret;
>  }
>  
> -static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp, bool writable)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	struct sev_user_data_pdh_cert_export input;
> @@ -708,7 +708,7 @@ static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
>  
>  	/* If platform is not in INIT state then transition it to INIT. */
>  	if (sev->state != SEV_STATE_INIT) {
> -		if (!capable(CAP_SYS_ADMIN))
> +		if (!writable)
>  			return -EPERM;
>  
>  		ret = __sev_platform_init_locked(&argp->error);
> @@ -801,6 +801,7 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
>  	void __user *argp = (void __user *)arg;
>  	struct sev_issue_cmd input;
>  	int ret = -EFAULT;
> +	bool writable = file->f_mode & FMODE_WRITE;
>  
>  	if (!psp_master || !psp_master->sev_data)
>  		return -ENODEV;
> @@ -819,25 +820,25 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
>  	switch (input.cmd) {
>  
>  	case SEV_FACTORY_RESET:
> -		ret = sev_ioctl_do_reset(&input);
> +		ret = sev_ioctl_do_reset(&input, writable);
>  		break;
>  	case SEV_PLATFORM_STATUS:
>  		ret = sev_ioctl_do_platform_status(&input);
>  		break;
>  	case SEV_PEK_GEN:
> -		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input);
> +		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input, writable);
>  		break;
>  	case SEV_PDH_GEN:
> -		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input);
> +		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input, writable);
>  		break;
>  	case SEV_PEK_CSR:
> -		ret = sev_ioctl_do_pek_csr(&input);
> +		ret = sev_ioctl_do_pek_csr(&input, writable);
>  		break;
>  	case SEV_PEK_CERT_IMPORT:
> -		ret = sev_ioctl_do_pek_import(&input);
> +		ret = sev_ioctl_do_pek_import(&input, writable);
>  		break;
>  	case SEV_PDH_CERT_EXPORT:
> -		ret = sev_ioctl_do_pdh_export(&input);
> +		ret = sev_ioctl_do_pdh_export(&input, writable);
>  		break;
>  	case SEV_GET_ID:
>  		pr_warn_once("SEV_GET_ID command is deprecated, use SEV_GET_ID2\n");
> -- 
> 2.24.1
> 
> 

Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[Nathaniel McCallum]

On Sun, Mar 8, 2020 at 5:54 PM David Rientjes <rientjes@google.com> wrote:
>
> On Fri, 6 Mar 2020, Connor Kuehl wrote:
>
> > Instead of using CAP_SYS_ADMIN which is restricted to the root user,
> > check the file mode for write permissions before executing commands that
> > can affect the platform. This allows for more fine-grained access
> > control to the SEV ioctl interface. This would allow a SEV-only user
> > or group the ability to administer the platform without requiring them
> > to be root or granting them overly powerful permissions.
> >
> > For example:
> >
> > chown root:root /dev/sev
> > chmod 600 /dev/sev
>
> Hi Connor,
>
> I'm curious why do you need to do the two above commands?  It implies that
> /dev/sev is either not owned by root or that it is not already restricted
> to only being owner read and writable.
>
> Or perhaps these two commands were included only for clarity to explain
> what the defaults should be?

Correct. Those are just exemplary. They represent the existing permissions.

> > setfacl -m g:sev:r /dev/sev
> > setfacl -m g:sev-admin:rw /dev/sev
> >
> > In this instance, members of the "sev-admin" group have the ability to
> > perform all ioctl calls (including the ones that modify platform state).
> > Members of the "sev" group only have access to the ioctls that do not
> > modify the platform state.
> >
> > This also makes opening "/dev/sev" more consistent with how file
> > descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
> > the file descriptor could be opened read-only but could still execute
> > ioctls that modify the platform state. This patch enforces that the file
> > descriptor is opened with write privileges if it is going to be used to
> > modify the platform state.
> >
> > This flexibility is completely opt-in, and if it is not desirable by
> > the administrator then they do not need to give anyone else access to
> > /dev/sev.
> >
> > Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> > ---
> >  drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
> >  1 file changed, 17 insertions(+), 16 deletions(-)
> >
> > diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> > index e467860f797d..416b80938a3e 100644
> > --- a/drivers/crypto/ccp/sev-dev.c
> > +++ b/drivers/crypto/ccp/sev-dev.c
> > @@ -283,11 +283,11 @@ static int sev_get_platform_state(int *state, int *error)
> >       return rc;
> >  }
> >
> > -static int sev_ioctl_do_reset(struct sev_issue_cmd *argp)
> > +static int sev_ioctl_do_reset(struct sev_issue_cmd *argp, bool writable)
> >  {
> >       int state, rc;
> >
> > -     if (!capable(CAP_SYS_ADMIN))
> > +     if (!writable)
> >               return -EPERM;
> >
> >       /*
> > @@ -331,12 +331,12 @@ static int sev_ioctl_do_platform_status(struct sev_issue_cmd *argp)
> >       return ret;
> >  }
> >
> > -static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
> > +static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp, bool writable)
> >  {
> >       struct sev_device *sev = psp_master->sev_data;
> >       int rc;
> >
> > -     if (!capable(CAP_SYS_ADMIN))
> > +     if (!writable)
> >               return -EPERM;
> >
> >       if (sev->state == SEV_STATE_UNINIT) {
> > @@ -348,7 +348,7 @@ static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
> >       return __sev_do_cmd_locked(cmd, NULL, &argp->error);
> >  }
> >
> > -static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
> > +static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp, bool writable)
> >  {
> >       struct sev_device *sev = psp_master->sev_data;
> >       struct sev_user_data_pek_csr input;
> > @@ -356,7 +356,7 @@ static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
> >       void *blob = NULL;
> >       int ret;
> >
> > -     if (!capable(CAP_SYS_ADMIN))
> > +     if (!writable)
> >               return -EPERM;
> >
> >       if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> > @@ -539,7 +539,7 @@ static int sev_update_firmware(struct device *dev)
> >       return ret;
> >  }
> >
> > -static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
> > +static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp, bool writable)
> >  {
> >       struct sev_device *sev = psp_master->sev_data;
> >       struct sev_user_data_pek_cert_import input;
> > @@ -547,7 +547,7 @@ static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
> >       void *pek_blob, *oca_blob;
> >       int ret;
> >
> > -     if (!capable(CAP_SYS_ADMIN))
> > +     if (!writable)
> >               return -EPERM;
> >
> >       if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> > @@ -698,7 +698,7 @@ static int sev_ioctl_do_get_id(struct sev_issue_cmd *argp)
> >       return ret;
> >  }
> >
> > -static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
> > +static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp, bool writable)
> >  {
> >       struct sev_device *sev = psp_master->sev_data;
> >       struct sev_user_data_pdh_cert_export input;
> > @@ -708,7 +708,7 @@ static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
> >
> >       /* If platform is not in INIT state then transition it to INIT. */
> >       if (sev->state != SEV_STATE_INIT) {
> > -             if (!capable(CAP_SYS_ADMIN))
> > +             if (!writable)
> >                       return -EPERM;
> >
> >               ret = __sev_platform_init_locked(&argp->error);
> > @@ -801,6 +801,7 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> >       void __user *argp = (void __user *)arg;
> >       struct sev_issue_cmd input;
> >       int ret = -EFAULT;
> > +     bool writable = file->f_mode & FMODE_WRITE;
> >
> >       if (!psp_master || !psp_master->sev_data)
> >               return -ENODEV;
> > @@ -819,25 +820,25 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> >       switch (input.cmd) {
> >
> >       case SEV_FACTORY_RESET:
> > -             ret = sev_ioctl_do_reset(&input);
> > +             ret = sev_ioctl_do_reset(&input, writable);
> >               break;
> >       case SEV_PLATFORM_STATUS:
> >               ret = sev_ioctl_do_platform_status(&input);
> >               break;
> >       case SEV_PEK_GEN:
> > -             ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input);
> > +             ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input, writable);
> >               break;
> >       case SEV_PDH_GEN:
> > -             ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input);
> > +             ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input, writable);
> >               break;
> >       case SEV_PEK_CSR:
> > -             ret = sev_ioctl_do_pek_csr(&input);
> > +             ret = sev_ioctl_do_pek_csr(&input, writable);
> >               break;
> >       case SEV_PEK_CERT_IMPORT:
> > -             ret = sev_ioctl_do_pek_import(&input);
> > +             ret = sev_ioctl_do_pek_import(&input, writable);
> >               break;
> >       case SEV_PDH_CERT_EXPORT:
> > -             ret = sev_ioctl_do_pdh_export(&input);
> > +             ret = sev_ioctl_do_pdh_export(&input, writable);
> >               break;
> >       case SEV_GET_ID:
> >               pr_warn_once("SEV_GET_ID command is deprecated, use SEV_GET_ID2\n");
> > --
> > 2.24.1
> >
> >
>

Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[David Rientjes]

On Mon, 9 Mar 2020, Nathaniel McCallum wrote:

> > > Instead of using CAP_SYS_ADMIN which is restricted to the root user,
> > > check the file mode for write permissions before executing commands that
> > > can affect the platform. This allows for more fine-grained access
> > > control to the SEV ioctl interface. This would allow a SEV-only user
> > > or group the ability to administer the platform without requiring them
> > > to be root or granting them overly powerful permissions.
> > >
> > > For example:
> > >
> > > chown root:root /dev/sev
> > > chmod 600 /dev/sev
> >
> > Hi Connor,
> >
> > I'm curious why do you need to do the two above commands?  It implies that
> > /dev/sev is either not owned by root or that it is not already restricted
> > to only being owner read and writable.
> >
> > Or perhaps these two commands were included only for clarity to explain
> > what the defaults should be?
> 
> Correct. Those are just exemplary. They represent the existing permissions.
> 

Sounds good, thanks.  Maybe showing what ls -l /dev/sev looks like by 
default in the changelog would make it clear.  Otherwise looks good.

> > > setfacl -m g:sev:r /dev/sev
> > > setfacl -m g:sev-admin:rw /dev/sev
> > >
> > > In this instance, members of the "sev-admin" group have the ability to
> > > perform all ioctl calls (including the ones that modify platform state).
> > > Members of the "sev" group only have access to the ioctls that do not
> > > modify the platform state.
> > >
> > > This also makes opening "/dev/sev" more consistent with how file
> > > descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
> > > the file descriptor could be opened read-only but could still execute
> > > ioctls that modify the platform state. This patch enforces that the file
> > > descriptor is opened with write privileges if it is going to be used to
> > > modify the platform state.
> > >
> > > This flexibility is completely opt-in, and if it is not desirable by
> > > the administrator then they do not need to give anyone else access to
> > > /dev/sev.
> > >
> > > Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> > > ---
> > >  drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
> > >  1 file changed, 17 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> > > index e467860f797d..416b80938a3e 100644
> > > --- a/drivers/crypto/ccp/sev-dev.c
> > > +++ b/drivers/crypto/ccp/sev-dev.c
> > > @@ -283,11 +283,11 @@ static int sev_get_platform_state(int *state, int *error)
> > >       return rc;
> > >  }
> > >
> > > -static int sev_ioctl_do_reset(struct sev_issue_cmd *argp)
> > > +static int sev_ioctl_do_reset(struct sev_issue_cmd *argp, bool writable)
> > >  {
> > >       int state, rc;
> > >
> > > -     if (!capable(CAP_SYS_ADMIN))
> > > +     if (!writable)
> > >               return -EPERM;
> > >
> > >       /*
> > > @@ -331,12 +331,12 @@ static int sev_ioctl_do_platform_status(struct sev_issue_cmd *argp)
> > >       return ret;
> > >  }
> > >
> > > -static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
> > > +static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp, bool writable)
> > >  {
> > >       struct sev_device *sev = psp_master->sev_data;
> > >       int rc;
> > >
> > > -     if (!capable(CAP_SYS_ADMIN))
> > > +     if (!writable)
> > >               return -EPERM;
> > >
> > >       if (sev->state == SEV_STATE_UNINIT) {
> > > @@ -348,7 +348,7 @@ static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
> > >       return __sev_do_cmd_locked(cmd, NULL, &argp->error);
> > >  }
> > >
> > > -static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
> > > +static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp, bool writable)
> > >  {
> > >       struct sev_device *sev = psp_master->sev_data;
> > >       struct sev_user_data_pek_csr input;
> > > @@ -356,7 +356,7 @@ static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
> > >       void *blob = NULL;
> > >       int ret;
> > >
> > > -     if (!capable(CAP_SYS_ADMIN))
> > > +     if (!writable)
> > >               return -EPERM;
> > >
> > >       if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> > > @@ -539,7 +539,7 @@ static int sev_update_firmware(struct device *dev)
> > >       return ret;
> > >  }
> > >
> > > -static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
> > > +static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp, bool writable)
> > >  {
> > >       struct sev_device *sev = psp_master->sev_data;
> > >       struct sev_user_data_pek_cert_import input;
> > > @@ -547,7 +547,7 @@ static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
> > >       void *pek_blob, *oca_blob;
> > >       int ret;
> > >
> > > -     if (!capable(CAP_SYS_ADMIN))
> > > +     if (!writable)
> > >               return -EPERM;
> > >
> > >       if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> > > @@ -698,7 +698,7 @@ static int sev_ioctl_do_get_id(struct sev_issue_cmd *argp)
> > >       return ret;
> > >  }
> > >
> > > -static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
> > > +static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp, bool writable)
> > >  {
> > >       struct sev_device *sev = psp_master->sev_data;
> > >       struct sev_user_data_pdh_cert_export input;
> > > @@ -708,7 +708,7 @@ static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
> > >
> > >       /* If platform is not in INIT state then transition it to INIT. */
> > >       if (sev->state != SEV_STATE_INIT) {
> > > -             if (!capable(CAP_SYS_ADMIN))
> > > +             if (!writable)
> > >                       return -EPERM;
> > >
> > >               ret = __sev_platform_init_locked(&argp->error);
> > > @@ -801,6 +801,7 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> > >       void __user *argp = (void __user *)arg;
> > >       struct sev_issue_cmd input;
> > >       int ret = -EFAULT;
> > > +     bool writable = file->f_mode & FMODE_WRITE;
> > >
> > >       if (!psp_master || !psp_master->sev_data)
> > >               return -ENODEV;
> > > @@ -819,25 +820,25 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
> > >       switch (input.cmd) {
> > >
> > >       case SEV_FACTORY_RESET:
> > > -             ret = sev_ioctl_do_reset(&input);
> > > +             ret = sev_ioctl_do_reset(&input, writable);
> > >               break;
> > >       case SEV_PLATFORM_STATUS:
> > >               ret = sev_ioctl_do_platform_status(&input);
> > >               break;
> > >       case SEV_PEK_GEN:
> > > -             ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input);
> > > +             ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input, writable);
> > >               break;
> > >       case SEV_PDH_GEN:
> > > -             ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input);
> > > +             ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input, writable);
> > >               break;
> > >       case SEV_PEK_CSR:
> > > -             ret = sev_ioctl_do_pek_csr(&input);
> > > +             ret = sev_ioctl_do_pek_csr(&input, writable);
> > >               break;
> > >       case SEV_PEK_CERT_IMPORT:
> > > -             ret = sev_ioctl_do_pek_import(&input);
> > > +             ret = sev_ioctl_do_pek_import(&input, writable);
> > >               break;
> > >       case SEV_PDH_CERT_EXPORT:
> > > -             ret = sev_ioctl_do_pdh_export(&input);
> > > +             ret = sev_ioctl_do_pdh_export(&input, writable);
> > >               break;
> > >       case SEV_GET_ID:
> > >               pr_warn_once("SEV_GET_ID command is deprecated, use SEV_GET_ID2\n");
> > > --
> > > 2.24.1
> > >
> > >
> >
> 
> 

Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[Brijesh Singh]

On 3/6/20 11:20 AM, Connor Kuehl wrote:
> Instead of using CAP_SYS_ADMIN which is restricted to the root user,
> check the file mode for write permissions before executing commands that
> can affect the platform. This allows for more fine-grained access
> control to the SEV ioctl interface. This would allow a SEV-only user
> or group the ability to administer the platform without requiring them
> to be root or granting them overly powerful permissions.
> 
> For example:
> 
> chown root:root /dev/sev
> chmod 600 /dev/sev
> setfacl -m g:sev:r /dev/sev
> setfacl -m g:sev-admin:rw /dev/sev
> 
> In this instance, members of the "sev-admin" group have the ability to
> perform all ioctl calls (including the ones that modify platform state).
> Members of the "sev" group only have access to the ioctls that do not
> modify the platform state.
> 
> This also makes opening "/dev/sev" more consistent with how file
> descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
> the file descriptor could be opened read-only but could still execute
> ioctls that modify the platform state. This patch enforces that the file
> descriptor is opened with write privileges if it is going to be used to
> modify the platform state.
> 
> This flexibility is completely opt-in, and if it is not desirable by
> the administrator then they do not need to give anyone else access to
> /dev/sev.
> 
> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> ---
>   drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
>   1 file changed, 17 insertions(+), 16 deletions(-)
> 

Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>

thanks

Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[Bandan Das]

Brijesh Singh <brijesh.singh@amd.com> writes:

> On 3/6/20 11:20 AM, Connor Kuehl wrote:
>> Instead of using CAP_SYS_ADMIN which is restricted to the root user,
>> check the file mode for write permissions before executing commands that
>> can affect the platform. This allows for more fine-grained access
>> control to the SEV ioctl interface. This would allow a SEV-only user
>> or group the ability to administer the platform without requiring them
>> to be root or granting them overly powerful permissions.
>>
>> For example:
>>
>> chown root:root /dev/sev
>> chmod 600 /dev/sev
>> setfacl -m g:sev:r /dev/sev
>> setfacl -m g:sev-admin:rw /dev/sev
>>
>> In this instance, members of the "sev-admin" group have the ability to
>> perform all ioctl calls (including the ones that modify platform state).
>> Members of the "sev" group only have access to the ioctls that do not
>> modify the platform state.
>>
>> This also makes opening "/dev/sev" more consistent with how file
>> descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
>> the file descriptor could be opened read-only but could still execute
>> ioctls that modify the platform state. This patch enforces that the file
>> descriptor is opened with write privileges if it is going to be used to
>> modify the platform state.
>>
>> This flexibility is completely opt-in, and if it is not desirable by
>> the administrator then they do not need to give anyone else access to
>> /dev/sev.
>>
>> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
>> ---
>>   drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
>>   1 file changed, 17 insertions(+), 16 deletions(-)
>>
>
> Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
>
> thanks

Reviewed-by: Bandan Das <bsd@redhat.com>

Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[David Rientjes]

On Tue, 10 Mar 2020, Bandan Das wrote:

> Brijesh Singh <brijesh.singh@amd.com> writes:
> 
> > On 3/6/20 11:20 AM, Connor Kuehl wrote:
> >> Instead of using CAP_SYS_ADMIN which is restricted to the root user,
> >> check the file mode for write permissions before executing commands that
> >> can affect the platform. This allows for more fine-grained access
> >> control to the SEV ioctl interface. This would allow a SEV-only user
> >> or group the ability to administer the platform without requiring them
> >> to be root or granting them overly powerful permissions.
> >>
> >> For example:
> >>
> >> chown root:root /dev/sev
> >> chmod 600 /dev/sev
> >> setfacl -m g:sev:r /dev/sev
> >> setfacl -m g:sev-admin:rw /dev/sev
> >>
> >> In this instance, members of the "sev-admin" group have the ability to
> >> perform all ioctl calls (including the ones that modify platform state).
> >> Members of the "sev" group only have access to the ioctls that do not
> >> modify the platform state.
> >>
> >> This also makes opening "/dev/sev" more consistent with how file
> >> descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
> >> the file descriptor could be opened read-only but could still execute
> >> ioctls that modify the platform state. This patch enforces that the file
> >> descriptor is opened with write privileges if it is going to be used to
> >> modify the platform state.
> >>
> >> This flexibility is completely opt-in, and if it is not desirable by
> >> the administrator then they do not need to give anyone else access to
> >> /dev/sev.
> >>
> >> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> >> ---
> >>   drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
> >>   1 file changed, 17 insertions(+), 16 deletions(-)
> >>
> >
> > Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>
> >
> > thanks
> 
> Reviewed-by: Bandan Das <bsd@redhat.com>
> 

Acked-by: David Rientjes <rientjes@google.com>

Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[Tom Lendacky]

On 3/6/20 11:20 AM, Connor Kuehl wrote:
> Instead of using CAP_SYS_ADMIN which is restricted to the root user,
> check the file mode for write permissions before executing commands that
> can affect the platform. This allows for more fine-grained access
> control to the SEV ioctl interface. This would allow a SEV-only user
> or group the ability to administer the platform without requiring them
> to be root or granting them overly powerful permissions.
> 
> For example:
> 
> chown root:root /dev/sev
> chmod 600 /dev/sev
> setfacl -m g:sev:r /dev/sev
> setfacl -m g:sev-admin:rw /dev/sev
> 
> In this instance, members of the "sev-admin" group have the ability to
> perform all ioctl calls (including the ones that modify platform state).
> Members of the "sev" group only have access to the ioctls that do not
> modify the platform state.
> 
> This also makes opening "/dev/sev" more consistent with how file
> descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
> the file descriptor could be opened read-only but could still execute
> ioctls that modify the platform state. This patch enforces that the file
> descriptor is opened with write privileges if it is going to be used to
> modify the platform state.
> 
> This flexibility is completely opt-in, and if it is not desirable by
> the administrator then they do not need to give anyone else access to
> /dev/sev.
> 
> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>

Acked-by: Tom Lendacky <thomas.lendacky@amd.com>

> ---
>  drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index e467860f797d..416b80938a3e 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -283,11 +283,11 @@ static int sev_get_platform_state(int *state, int *error)
>  	return rc;
>  }
>  
> -static int sev_ioctl_do_reset(struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_reset(struct sev_issue_cmd *argp, bool writable)
>  {
>  	int state, rc;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!writable)
>  		return -EPERM;
>  
>  	/*
> @@ -331,12 +331,12 @@ static int sev_ioctl_do_platform_status(struct sev_issue_cmd *argp)
>  	return ret;
>  }
>  
> -static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp, bool writable)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	int rc;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!writable)
>  		return -EPERM;
>  
>  	if (sev->state == SEV_STATE_UNINIT) {
> @@ -348,7 +348,7 @@ static int sev_ioctl_do_pek_pdh_gen(int cmd, struct sev_issue_cmd *argp)
>  	return __sev_do_cmd_locked(cmd, NULL, &argp->error);
>  }
>  
> -static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp, bool writable)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	struct sev_user_data_pek_csr input;
> @@ -356,7 +356,7 @@ static int sev_ioctl_do_pek_csr(struct sev_issue_cmd *argp)
>  	void *blob = NULL;
>  	int ret;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!writable)
>  		return -EPERM;
>  
>  	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> @@ -539,7 +539,7 @@ static int sev_update_firmware(struct device *dev)
>  	return ret;
>  }
>  
> -static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp, bool writable)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	struct sev_user_data_pek_cert_import input;
> @@ -547,7 +547,7 @@ static int sev_ioctl_do_pek_import(struct sev_issue_cmd *argp)
>  	void *pek_blob, *oca_blob;
>  	int ret;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!writable)
>  		return -EPERM;
>  
>  	if (copy_from_user(&input, (void __user *)argp->data, sizeof(input)))
> @@ -698,7 +698,7 @@ static int sev_ioctl_do_get_id(struct sev_issue_cmd *argp)
>  	return ret;
>  }
>  
> -static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
> +static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp, bool writable)
>  {
>  	struct sev_device *sev = psp_master->sev_data;
>  	struct sev_user_data_pdh_cert_export input;
> @@ -708,7 +708,7 @@ static int sev_ioctl_do_pdh_export(struct sev_issue_cmd *argp)
>  
>  	/* If platform is not in INIT state then transition it to INIT. */
>  	if (sev->state != SEV_STATE_INIT) {
> -		if (!capable(CAP_SYS_ADMIN))
> +		if (!writable)
>  			return -EPERM;
>  
>  		ret = __sev_platform_init_locked(&argp->error);
> @@ -801,6 +801,7 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
>  	void __user *argp = (void __user *)arg;
>  	struct sev_issue_cmd input;
>  	int ret = -EFAULT;
> +	bool writable = file->f_mode & FMODE_WRITE;
>  
>  	if (!psp_master || !psp_master->sev_data)
>  		return -ENODEV;
> @@ -819,25 +820,25 @@ static long sev_ioctl(struct file *file, unsigned int ioctl, unsigned long arg)
>  	switch (input.cmd) {
>  
>  	case SEV_FACTORY_RESET:
> -		ret = sev_ioctl_do_reset(&input);
> +		ret = sev_ioctl_do_reset(&input, writable);
>  		break;
>  	case SEV_PLATFORM_STATUS:
>  		ret = sev_ioctl_do_platform_status(&input);
>  		break;
>  	case SEV_PEK_GEN:
> -		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input);
> +		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PEK_GEN, &input, writable);
>  		break;
>  	case SEV_PDH_GEN:
> -		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input);
> +		ret = sev_ioctl_do_pek_pdh_gen(SEV_CMD_PDH_GEN, &input, writable);
>  		break;
>  	case SEV_PEK_CSR:
> -		ret = sev_ioctl_do_pek_csr(&input);
> +		ret = sev_ioctl_do_pek_csr(&input, writable);
>  		break;
>  	case SEV_PEK_CERT_IMPORT:
> -		ret = sev_ioctl_do_pek_import(&input);
> +		ret = sev_ioctl_do_pek_import(&input, writable);
>  		break;
>  	case SEV_PDH_CERT_EXPORT:
> -		ret = sev_ioctl_do_pdh_export(&input);
> +		ret = sev_ioctl_do_pdh_export(&input, writable);
>  		break;
>  	case SEV_GET_ID:
>  		pr_warn_once("SEV_GET_ID command is deprecated, use SEV_GET_ID2\n");
> 

Re: [PATCH 1/1] crypto: ccp: use file mode for sev ioctl permissions

[Herbert Xu]

On Fri, Mar 06, 2020 at 09:20:10AM -0800, Connor Kuehl wrote:
> Instead of using CAP_SYS_ADMIN which is restricted to the root user,
> check the file mode for write permissions before executing commands that
> can affect the platform. This allows for more fine-grained access
> control to the SEV ioctl interface. This would allow a SEV-only user
> or group the ability to administer the platform without requiring them
> to be root or granting them overly powerful permissions.
> 
> For example:
> 
> chown root:root /dev/sev
> chmod 600 /dev/sev
> setfacl -m g:sev:r /dev/sev
> setfacl -m g:sev-admin:rw /dev/sev
> 
> In this instance, members of the "sev-admin" group have the ability to
> perform all ioctl calls (including the ones that modify platform state).
> Members of the "sev" group only have access to the ioctls that do not
> modify the platform state.
> 
> This also makes opening "/dev/sev" more consistent with how file
> descriptors are usually handled. By only checking for CAP_SYS_ADMIN,
> the file descriptor could be opened read-only but could still execute
> ioctls that modify the platform state. This patch enforces that the file
> descriptor is opened with write privileges if it is going to be used to
> modify the platform state.
> 
> This flexibility is completely opt-in, and if it is not desirable by
> the administrator then they do not need to give anyone else access to
> /dev/sev.
> 
> Signed-off-by: Connor Kuehl <ckuehl@redhat.com>
> ---
>  drivers/crypto/ccp/sev-dev.c | 33 +++++++++++++++++----------------
>  1 file changed, 17 insertions(+), 16 deletions(-)

Patch applied.  Thanks.
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt