kernel.git/arch/x86/kernel/xsave.c, branch linux-3.18.y

x86/fpu: Don't let userspace set bogus xcomp_bv

2017-10-05T07:35:52Z

commit 814fb7bb7db5433757d76f4c4502c96fc53b0b5e upstream. [Please apply to 3.18-stable. Note: the backport includes the fpu_finit() call in xstateregs_set(), since fix is useless without it. It was added by commit 91c3dba7dbc1 ("x86/fpu/xstate: Fix PTRACE frames for XSAVES"), but it doesn't make sense to backport that whole commit.] On x86, userspace can use the ptrace() or rt_sigreturn() system calls to set a task's extended state (xstate) or "FPU" registers. ptrace() can set them for another task using the PTRACE_SETREGSET request with NT_X86_XSTATE, while rt_sigreturn() can set them for the current task. In either case, registers can be set to any value, but the kernel assumes that the XSAVE area itself remains valid in the sense that the CPU can restore it. However, in the case where the kernel is using the uncompacted xstate format (which it does whenever the XSAVES instruction is unavailable), it was possible for userspace to set the xcomp_bv field in the xstate_header to an arbitrary value. However, all bits in that field are reserved in the uncompacted case, so when switching to a task with nonzero xcomp_bv, the XRSTOR instruction failed with a #GP fault. This caused the WARN_ON_FPU(err) in copy_kernel_to_xregs() to be hit. In addition, since the error is otherwise ignored, the FPU registers from the task previously executing on the CPU were leaked. Fix the bug by checking that the user-supplied value of xcomp_bv is 0 in the uncompacted case, and returning an error otherwise. The reason for validating xcomp_bv rather than simply overwriting it with 0 is that we want userspace to see an error if it (incorrectly) provides an XSAVE area in compacted format rather than in uncompacted format. Note that as before, in case of error we clear the task's FPU state. This is perhaps non-ideal, especially for PTRACE_SETREGSET; it might be better to return an error before changing anything. But it seems the "clear on error" behavior is fine for now, and it's a little tricky to do otherwise because it would mean we couldn't simply copy the full userspace state into kernel memory in one __copy_from_user(). This bug was found by syzkaller, which hit the above-mentioned WARN_ON_FPU(): WARNING: CPU: 1 PID: 0 at ./arch/x86/include/asm/fpu/internal.h:373 __switch_to+0x5b5/0x5d0 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.13.0 #453 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 task: ffff9ba2bc8e42c0 task.stack: ffffa78cc036c000 RIP: 0010:__switch_to+0x5b5/0x5d0 RSP: 0000:ffffa78cc08bbb88 EFLAGS: 00010082 RAX: 00000000fffffffe RBX: ffff9ba2b8bf2180 RCX: 00000000c0000100 RDX: 00000000ffffffff RSI: 000000005cb10700 RDI: ffff9ba2b8bf36c0 RBP: ffffa78cc08bbbd0 R08: 00000000929fdf46 R09: 0000000000000001 R10: 0000000000000000 R11: 0000000000000000 R12: ffff9ba2bc8e42c0 R13: 0000000000000000 R14: ffff9ba2b8bf3680 R15: ffff9ba2bf5d7b40 FS: 00007f7e5cb10700(0000) GS:ffff9ba2bf400000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000000004005cc CR3: 0000000079fd5000 CR4: 00000000001406e0 Call Trace: Code: 84 00 00 00 00 00 e9 11 fd ff ff 0f ff 66 0f 1f 84 00 00 00 00 00 e9 e7 fa ff ff 0f ff 66 0f 1f 84 00 00 00 00 00 e9 c2 fa ff ff <0f> ff 66 0f 1f 84 00 00 00 00 00 e9 d4 fc ff ff 66 66 2e 0f 1f Here is a C reproducer. The expected behavior is that the program spin forever with no output. However, on a buggy kernel running on a processor with the "xsave" feature but without the "xsaves" feature (e.g. Sandy Bridge through Broadwell for Intel), within a second or two the program reports that the xmm registers were corrupted, i.e. were not restored correctly. With CONFIG_X86_DEBUG_FPU=y it also hits the above kernel warning. #define _GNU_SOURCE #include #include #include #include #include #include #include #include int main(void) { int pid = fork(); uint64_t xstate[512]; struct iovec iov = { .iov_base = xstate, .iov_len = sizeof(xstate) }; if (pid == 0) { bool tracee = true; for (int i = 0; i < sysconf(_SC_NPROCESSORS_ONLN) && tracee; i++) tracee = (fork() != 0); uint32_t xmm0[4] = { [0 ... 3] = tracee ? 0x00000000 : 0xDEADBEEF }; asm volatile(" movdqu %0, %%xmm0\n" " mov %0, %%rbx\n" "1: movdqu %%xmm0, %0\n" " mov %0, %%rax\n" " cmp %%rax, %%rbx\n" " je 1b\n" : "+m" (xmm0) : : "rax", "rbx", "xmm0"); printf("BUG: xmm registers corrupted! tracee=%d, xmm0=%08X%08X%08X%08X\n", tracee, xmm0[0], xmm0[1], xmm0[2], xmm0[3]); } else { usleep(100000); ptrace(PTRACE_ATTACH, pid, 0, 0); wait(NULL); ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov); xstate[65] = -1; ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov); ptrace(PTRACE_CONT, pid, 0, 0); wait(NULL); } return 1; } Note: the program only tests for the bug using the ptrace() system call. The bug can also be reproduced using the rt_sigreturn() system call, but only when called from a 32-bit program, since for 64-bit programs the kernel restores the FPU state from the signal frame by doing XRSTOR directly from userspace memory (with proper error checking). Reported-by: Dmitry Vyukov Signed-off-by: Eric Biggers Reviewed-by: Kees Cook Reviewed-by: Rik van Riel Acked-by: Dave Hansen Cc: Andrew Morton Cc: Andy Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Eric Biggers Cc: Fenghua Yu Cc: Kevin Hao Cc: Linus Torvalds Cc: Michael Halcrow Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Wanpeng Li Cc: Yu-cheng Yu Cc: kernel-hardening@lists.openwall.com Fixes: 0b29643a5843 ("x86/xsaves: Change compacted format xsave area header") Link: http://lkml.kernel.org/r/20170922174156.16780-2-ebiggers3@gmail.com Link: http://lkml.kernel.org/r/20170923130016.21448-25-mingo@kernel.org Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman

x86: Clean up cr4 manipulation

2015-06-28T17:39:27Z

[ Upstream commit 375074cc736ab1d89a708c0a8d7baa4a70d5d476 ] CR4 manipulation was split, seemingly at random, between direct (write_cr4) and using a helper (set/clear_in_cr4). Unfortunately, the set_in_cr4 and clear_in_cr4 helpers also poke at the boot code, which only a small subset of users actually wanted. This patch replaces all cr4 access in functions that don't leave cr4 exactly the way they found it with new helpers cr4_set_bits, cr4_clear_bits, and cr4_set_bits_and_update_boot. Signed-off-by: Andy Lutomirski Reviewed-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Cc: Andrea Arcangeli Cc: Vince Weaver Cc: "hillf.zj" Cc: Valdis Kletnieks Cc: Paul Mackerras Cc: Arnaldo Carvalho de Melo Cc: Kees Cook Cc: Linus Torvalds Link: http://lkml.kernel.org/r/495a10bdc9e67016b8fd3945700d46cfd5c12c2f.1414190806.git.luto@amacapital.net Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin

x86/fpu: Avoid math_state_restore() without used_math() in __restore_xstate_sig()

2015-03-28T14:03:51Z

[ Upstream commit a7c80ebcac3068b1c3cb27d538d29558c30010c8 ] math_state_restore() assumes it is called with irqs disabled, but this is not true if the caller is __restore_xstate_sig(). This means that if ia32_fxstate == T and __copy_from_user() fails, __restore_xstate_sig() returns with irqs disabled too. This triggers: BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:41 dump_stack ___might_sleep ? _raw_spin_unlock_irqrestore __might_sleep down_read ? _raw_spin_unlock_irqrestore print_vma_addr signal_fault sys32_rt_sigreturn Change __restore_xstate_sig() to call set_used_math() unconditionally. This avoids enabling and disabling interrupts in math_state_restore(). If copy_from_user() fails, we can simply do fpu_finit() by hand. [ Note: this is only the first step. math_state_restore() should not check used_math(), it should set this flag. While init_fpu() should simply die. ] Signed-off-by: Oleg Nesterov Signed-off-by: Borislav Petkov Cc: Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Pekka Riikonen Cc: Quentin Casasnovas Cc: Rik van Riel Cc: Suresh Siddha Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20150307153844.GB25954@redhat.com Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin

x86: export get_xsave_addr

2015-01-16T14:59:49Z

commit ba7b39203a3a18018173b87e73f27169bd8e5147 upstream. get_xsave_addr is the API to access XSAVE states, and KVM would like to use it. Export it. Cc: x86@kernel.org Cc: H. Peter Anvin Acked-by: Thomas Gleixner Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman

x86, fpu: __restore_xstate_sig()->math_state_restore() needs preempt_disable()

2014-09-02T21:51:15Z

Add preempt_disable() + preempt_enable() around math_state_restore() in __restore_xstate_sig(). Otherwise __switch_to() after __thread_fpu_begin() can overwrite fpu->state we are going to restore. Signed-off-by: Oleg Nesterov Link: http://lkml.kernel.org/r/20140902175717.GA21649@redhat.com Cc: # v3.7+ Reviewed-by: Suresh Siddha Signed-off-by: H. Peter Anvin

x86, fpu: shift drop_init_fpu() from save_xstate_sig() to handle_signal()

2014-09-02T21:51:14Z

save_xstate_sig()->drop_init_fpu() doesn't look right. setup_rt_frame() can fail after that, in this case the next setup_rt_frame() triggered by SIGSEGV won't save fpu simply because the old state was lost. This obviously mean that fpu won't be restored after sys_rt_sigreturn() from SIGSEGV handler. Shift drop_init_fpu() into !failed branch in handle_signal(). Test-case (needs -O2): #include #include #include #include #include #include #include volatile double D; void test(double d) { int pid = getpid(); for (D = d; D == d; ) { /* sys_tkill(pid, SIGHUP); asm to avoid save/reload * fp regs around "C" call */ asm ("" : : "a"(200), "D"(pid), "S"(1)); asm ("syscall" : : : "ax"); } printf("ERR!!\n"); } void sigh(int sig) { } char altstack[4096 * 10] __attribute__((aligned(4096))); void *tfunc(void *arg) { for (;;) { mprotect(altstack, sizeof(altstack), PROT_READ); mprotect(altstack, sizeof(altstack), PROT_READ|PROT_WRITE); } } int main(void) { stack_t st = { .ss_sp = altstack, .ss_size = sizeof(altstack), .ss_flags = SS_ONSTACK, }; struct sigaction sa = { .sa_handler = sigh, }; pthread_t pt; sigaction(SIGSEGV, &sa, NULL); sigaltstack(&st, NULL); sa.sa_flags = SA_ONSTACK; sigaction(SIGHUP, &sa, NULL); pthread_create(&pt, NULL, tfunc, NULL); test(123.456); return 0; } Reported-by: Bean Anderson Signed-off-by: Oleg Nesterov Link: http://lkml.kernel.org/r/20140902175713.GA21646@redhat.com Cc: # v3.7+ Signed-off-by: H. Peter Anvin

x86/xsaves: Clean up code in xstate offsets computation in xsave area

2014-05-31T00:12:41Z

This patch cleans up some code in xstate offsets computation in xsave area: 1. It changes xstate_comp_offsets as an array. This avoids possible NULL pointer caused by possible kmalloc() failure during boot time. 2. It changes the global variable xstate_comp_sizes to a local variable because it is used only in setup_xstate_comp(). 3. It adds missing offsets for FP and SSE in xsave area. Signed-off-by: Fenghua Yu Link: http://lkml.kernel.org/r/1401387164-43416-17-git-send-email-fenghua.yu@intel.com Signed-off-by: H. Peter Anvin

Define kernel API to get address of each state in xsave area

2014-05-29T21:33:09Z

In standard form, each state is saved in the xsave area in fixed offset. But in compacted form, offset of each saved state only can be calculated during run time because some xstates may not be enabled and saved. We define kernel API get_xsave_addr() returns address of a given state saved in a xsave area. It can be called in kernel to get address of each xstate in xsave area in either standard format or compacted format. It's useful when kernel wants to directly access each state in xsave area. Signed-off-by: Fenghua Yu Link: http://lkml.kernel.org/r/1401387164-43416-17-git-send-email-fenghua.yu@intel.com Signed-off-by: H. Peter Anvin

x86/xsaves: Enable xsaves/xrstors

2014-05-29T21:33:07Z

If xsaves/xrstors is enabled, compacted format of xsave area will be used and less memory may be used for context per process. And modified optimization implemented in xsaves/xrstors improves performance of saving xstate. Signed-off-by: Fenghua Yu Link: http://lkml.kernel.org/r/1401387164-43416-16-git-send-email-fenghua.yu@intel.com Signed-off-by: H. Peter Anvin

x86/xsaves: Call booting time xsaves and xrstors in setup_init_fpu_buf

2014-05-29T21:33:06Z

setup_init_fpu_buf() calls booting time xsaves and xrstors to save and restore xstate in xsave area. Signed-off-by: Fenghua Yu Link: http://lkml.kernel.org/r/1401387164-43416-15-git-send-email-fenghua.yu@intel.com Signed-off-by: H. Peter Anvin