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crypto: ccp - Fix the INIT_EX data file open failure

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There are 2 common cases when INIT_EX data file might not be
opened successfully and fail the sev initialization:

1. In user namespaces, normal user tasks (e.g. VMM) can change their
   current->fs->root to point to arbitrary directories. While
   init_ex_path is provided as a module param related to root file
   system. Solution: use the root directory of init_task to avoid
   accessing the wrong file.

2. Normal user tasks (e.g. VMM) don't have the privilege to access
   the INIT_EX data file. Solution: open the file as root and
   restore permissions immediately.

Fixes: 3d725965f8 ("crypto: ccp - Add SEV_INIT_EX support")
Signed-off-by: Jacky Li <jackyli@google.com>
Reviewed-by: Peter Gonda <pgonda@google.com>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Jacky Li 2022-04-14 16:23:25 +00:00 committed by Herbert Xu
parent c6d3ffae0d
commit 05def5cacf
1 changed files with 28 additions and 2 deletions
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30
drivers/crypto/ccp/sev-dev.c
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@ -23,6 +23,7 @@
#include <linux/gfp.h>
#include <linux/cpufeature.h>
#include <linux/fs.h>
#include <linux/fs_struct.h>
#include <asm/smp.h>
@ -170,6 +171,31 @@ static void *sev_fw_alloc(unsigned long len)
return page_address(page);
}
static struct file *open_file_as_root(const char *filename, int flags, umode_t mode)
{
struct file *fp;
struct path root;
struct cred *cred;
const struct cred *old_cred;
task_lock(&init_task);
get_fs_root(init_task.fs, &root);
task_unlock(&init_task);
cred = prepare_creds();
if (!cred)
return ERR_PTR(-ENOMEM);
cred->fsuid = GLOBAL_ROOT_UID;
old_cred = override_creds(cred);
fp = file_open_root(&root, filename, flags, mode);
path_put(&root);
revert_creds(old_cred);
return fp;
}
static int sev_read_init_ex_file(void)
{
struct sev_device *sev = psp_master->sev_data;
@ -181,7 +207,7 @@ static int sev_read_init_ex_file(void)
if (!sev_init_ex_buffer)
return -EOPNOTSUPP;
fp = filp_open(init_ex_path, O_RDONLY, 0);
fp = open_file_as_root(init_ex_path, O_RDONLY, 0);
if (IS_ERR(fp)) {
int ret = PTR_ERR(fp);
@ -217,7 +243,7 @@ static void sev_write_init_ex_file(void)
if (!sev_init_ex_buffer)
return;
fp = filp_open(init_ex_path, O_CREAT | O_WRONLY, 0600);
fp = open_file_as_root(init_ex_path, O_CREAT | O_WRONLY, 0600);
if (IS_ERR(fp)) {
dev_err(sev->dev,
"SEV: could not open file for write, error %ld\n",