diff options
| -rw-r--r-- | arch/x86/kernel/vm86_32.c | 27 | ||||
| -rw-r--r-- | tools/testing/selftests/x86/entry_from_vm86.c | 5 |
2 files changed, 30 insertions, 2 deletions
diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c index abd8b856bd2b..524619351961 100644 --- a/arch/x86/kernel/vm86_32.c +++ b/arch/x86/kernel/vm86_32.c @@ -45,6 +45,7 @@ #include <linux/audit.h> #include <linux/stddef.h> #include <linux/slab.h> +#include <linux/security.h> #include <asm/uaccess.h> #include <asm/io.h> @@ -232,6 +233,32 @@ static long do_sys_vm86(struct vm86plus_struct __user *user_vm86, bool plus) struct pt_regs *regs = current_pt_regs(); unsigned long err = 0; + err = security_mmap_addr(0); + if (err) { + /* + * vm86 cannot virtualize the address space, so vm86 users + * need to manage the low 1MB themselves using mmap. Given + * that BIOS places important data in the first page, vm86 + * is essentially useless if mmap_min_addr != 0. DOSEMU, + * for example, won't even bother trying to use vm86 if it + * can't map a page at virtual address 0. + * + * To reduce the available kernel attack surface, simply + * disallow vm86(old) for users who cannot mmap at va 0. + * + * The implementation of security_mmap_addr will allow + * suitably privileged users to map va 0 even if + * vm.mmap_min_addr is set above 0, and we want this + * behavior for vm86 as well, as it ensures that legacy + * tools like vbetool will not fail just because of + * vm.mmap_min_addr. + */ + pr_info_once("Denied a call to vm86(old) from %s[%d] (uid: %d). Set the vm.mmap_min_addr sysctl to 0 and/or adjust LSM mmap_min_addr policy to enable vm86 if you are using a vm86-based DOS emulator.\n", + current->comm, task_pid_nr(current), + from_kuid_munged(&init_user_ns, current_uid())); + return -EPERM; + } + if (!vm86) { if (!(vm86 = kzalloc(sizeof(*vm86), GFP_KERNEL))) return -ENOMEM; diff --git a/tools/testing/selftests/x86/entry_from_vm86.c b/tools/testing/selftests/x86/entry_from_vm86.c index 9a43a59a9bb4..421c607a8856 100644 --- a/tools/testing/selftests/x86/entry_from_vm86.c +++ b/tools/testing/selftests/x86/entry_from_vm86.c @@ -116,8 +116,9 @@ static bool do_test(struct vm86plus_struct *v86, unsigned long eip, v86->regs.eip = eip; ret = vm86(VM86_ENTER, v86); - if (ret == -1 && errno == ENOSYS) { - printf("[SKIP]\tvm86 not supported\n"); + if (ret == -1 && (errno == ENOSYS || errno == EPERM)) { + printf("[SKIP]\tvm86 %s\n", + errno == ENOSYS ? "not supported" : "not allowed"); return false; } |