From: Juergen Gross <jgross@suse.com> mainline inclusion from mainline-v7.0-rc6 commit 453b8fb68f3641fea970db88b7d9a153ed2a37e8 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/14027 CVE: CVE-2026-31788 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- The Xen privcmd driver allows to issue arbitrary hypercalls from user space processes. This is normally no problem, as access is usually limited to root and the hypervisor will deny any hypercalls affecting other domains. In case the guest is booted using secure boot, however, the privcmd driver would be enabling a root user process to modify e.g. kernel memory contents, thus breaking the secure boot feature. The only known case where an unprivileged domU is really needing to use the privcmd driver is the case when it is acting as the device model for another guest. In this case all hypercalls issued via the privcmd driver will target that other guest. Fortunately the privcmd driver can already be locked down to allow only hypercalls targeting a specific domain, but this mode can be activated from user land only today. The target domain can be obtained from Xenstore, so when not running in dom0 restrict the privcmd driver to that target domain from the beginning, resolving the potential problem of breaking secure boot. This is XSA-482 Reported-by: Teddy Astie <teddy.astie@vates.tech> Fixes: 1c5de1939c20 ("xen: add privcmd driver") Signed-off-by: Juergen Gross <jgross@suse.com> Conflicts: drivers/xen/privcmd.c [commit bf4afc53b77ae not merged] Signed-off-by: Zhang Yuwei <zhangyuwei20@huawei.com> it push" to publish your local commits) --- drivers/xen/privcmd.c | 62 +++++++++++++++++++++++++++++++++++++++---- 1 file changed, 57 insertions(+), 5 deletions(-) diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c index 28537a1a0e0b..cb50038c0c9c 100644 --- a/drivers/xen/privcmd.c +++ b/drivers/xen/privcmd.c @@ -10,6 +10,7 @@ #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt #include <linux/kernel.h> +#include <linux/kstrtox.h> #include <linux/module.h> #include <linux/sched.h> #include <linux/slab.h> @@ -24,7 +25,8 @@ #include <linux/seq_file.h> #include <linux/miscdevice.h> #include <linux/moduleparam.h> - +#include <linux/notifier.h> +#include <linux/wait.h> #include <asm/xen/hypervisor.h> #include <asm/xen/hypercall.h> @@ -37,7 +39,7 @@ #include <xen/page.h> #include <xen/xen-ops.h> #include <xen/balloon.h> - +#include <xen/xenbus.h> #include "privcmd.h" MODULE_LICENSE("GPL"); @@ -59,6 +61,11 @@ struct privcmd_data { domid_t domid; }; +/* DOMID_INVALID implies no restriction */ +static domid_t target_domain = DOMID_INVALID; +static bool restrict_wait; +static DECLARE_WAIT_QUEUE_HEAD(restrict_wait_wq); + static int privcmd_vma_range_is_mapped( struct vm_area_struct *vma, unsigned long addr, @@ -878,13 +885,16 @@ static long privcmd_ioctl(struct file *file, static int privcmd_open(struct inode *ino, struct file *file) { - struct privcmd_data *data = kzalloc(sizeof(*data), GFP_KERNEL); + struct privcmd_data *data; + if (wait_event_interruptible(restrict_wait_wq, !restrict_wait) < 0) + return -EINTR; + + data = kzalloc(sizeof(*data), GFP_KERNEL); if (!data) return -ENOMEM; - /* DOMID_INVALID implies no restriction */ - data->domid = DOMID_INVALID; + data->domid = target_domain; file->private_data = data; return 0; @@ -977,6 +987,45 @@ static struct miscdevice privcmd_dev = { .fops = &xen_privcmd_fops, }; +static int init_restrict(struct notifier_block *notifier, + unsigned long event, + void *data) +{ + char *target; + unsigned int domid; + + /* Default to an guaranteed unused domain-id. */ + target_domain = DOMID_IDLE; + + target = xenbus_read(XBT_NIL, "target", "", NULL); + if (IS_ERR(target) || kstrtouint(target, 10, &domid)) { + pr_err("No target domain found, blocking all hypercalls\n"); + goto out; + } + + target_domain = domid; + + out: + if (!IS_ERR(target)) + kfree(target); + + restrict_wait = false; + wake_up_all(&restrict_wait_wq); + + return NOTIFY_DONE; +} + +static struct notifier_block xenstore_notifier = { + .notifier_call = init_restrict, +}; + +static void __init restrict_driver(void) +{ + restrict_wait = true; + + register_xenstore_notifier(&xenstore_notifier); +} + static int __init privcmd_init(void) { int err; @@ -984,6 +1033,9 @@ static int __init privcmd_init(void) if (!xen_domain()) return -ENODEV; + if (!xen_initial_domain()) + restrict_driver(); + err = misc_register(&privcmd_dev); if (err != 0) { pr_err("Could not register Xen privcmd device\n"); -- 2.22.0