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@xxxxxxxxxx> Acked-by: Tom Lendacky <thomas.lendacky@xxxxxxx> > --- > 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"); >