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@xxxxxxxxxx> > > > --- > > > 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 > > > > > > > > > >