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authorDavid Hildenbrand <david@redhat.com>2017-11-07 12:04:05 -0500
committerPaolo Bonzini <pbonzini@redhat.com>2017-11-17 07:20:15 -0500
commit4d772cb85f64c16eca00177089ecb3cd5d292120 (patch)
treee1d42c7bcf88c9502cf35e118c26e50bbff634c9
parent5af4157388adad82c339e3742fb6b67840721347 (diff)
KVM: x86: fix em_fxstor() sleeping while in atomic
Commit 9d643f63128b ("KVM: x86: avoid large stack allocations in em_fxrstor") optimize the stack size, but introduced a guest memory access which might sleep while in atomic. Fix it by introducing, again, a second fxregs_state. Try to avoid large stacks by using noinline. Add some helpful comments. Reported by syzbot: in_atomic(): 1, irqs_disabled(): 0, pid: 2909, name: syzkaller879109 2 locks held by syzkaller879109/2909: #0: (&vcpu->mutex){+.+.}, at: [<ffffffff8106222c>] vcpu_load+0x1c/0x70 arch/x86/kvm/../../../virt/kvm/kvm_main.c:154 #1: (&kvm->srcu){....}, at: [<ffffffff810dd162>] vcpu_enter_guest arch/x86/kvm/x86.c:6983 [inline] #1: (&kvm->srcu){....}, at: [<ffffffff810dd162>] vcpu_run arch/x86/kvm/x86.c:7061 [inline] #1: (&kvm->srcu){....}, at: [<ffffffff810dd162>] kvm_arch_vcpu_ioctl_run+0x1bc2/0x58b0 arch/x86/kvm/x86.c:7222 CPU: 1 PID: 2909 Comm: syzkaller879109 Not tainted 4.13.0-rc4-next-20170811 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:16 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:52 ___might_sleep+0x2b2/0x470 kernel/sched/core.c:6014 __might_sleep+0x95/0x190 kernel/sched/core.c:5967 __might_fault+0xab/0x1d0 mm/memory.c:4383 __copy_from_user include/linux/uaccess.h:71 [inline] __kvm_read_guest_page+0x58/0xa0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1771 kvm_vcpu_read_guest_page+0x44/0x60 arch/x86/kvm/../../../virt/kvm/kvm_main.c:1791 kvm_read_guest_virt_helper+0x76/0x140 arch/x86/kvm/x86.c:4407 kvm_read_guest_virt_system+0x3c/0x50 arch/x86/kvm/x86.c:4466 segmented_read_std+0x10c/0x180 arch/x86/kvm/emulate.c:819 em_fxrstor+0x27b/0x410 arch/x86/kvm/emulate.c:4022 x86_emulate_insn+0x55d/0x3c50 arch/x86/kvm/emulate.c:5471 x86_emulate_instruction+0x411/0x1ca0 arch/x86/kvm/x86.c:5698 kvm_mmu_page_fault+0x18b/0x2c0 arch/x86/kvm/mmu.c:4854 handle_ept_violation+0x1fc/0x5e0 arch/x86/kvm/vmx.c:6400 vmx_handle_exit+0x281/0x1ab0 arch/x86/kvm/vmx.c:8718 vcpu_enter_guest arch/x86/kvm/x86.c:6999 [inline] vcpu_run arch/x86/kvm/x86.c:7061 [inline] kvm_arch_vcpu_ioctl_run+0x1cee/0x58b0 arch/x86/kvm/x86.c:7222 kvm_vcpu_ioctl+0x64c/0x1010 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2591 vfs_ioctl fs/ioctl.c:45 [inline] do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685 SYSC_ioctl fs/ioctl.c:700 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691 entry_SYSCALL_64_fastpath+0x1f/0xbe RIP: 0033:0x437fc9 RSP: 002b:00007ffc7b4d5ab8 EFLAGS: 00000206 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00000000004002b0 RCX: 0000000000437fc9 RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005 RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000020ae8000 R10: 0000000000009120 R11: 0000000000000206 R12: 0000000000000000 R13: 0000000000000004 R14: 0000000000000004 R15: 0000000020077000 Fixes: 9d643f63128b ("KVM: x86: avoid large stack allocations in em_fxrstor") Signed-off-by: David Hildenbrand <david@redhat.com> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
-rw-r--r--arch/x86/kvm/emulate.c32
1 files changed, 26 insertions, 6 deletions
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b4a87debbb4b..e7d04d0c8008 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4014,6 +4014,26 @@ static int em_fxsave(struct x86_emulate_ctxt *ctxt)
4014 fxstate_size(ctxt)); 4014 fxstate_size(ctxt));
4015} 4015}
4016 4016
4017/*
4018 * FXRSTOR might restore XMM registers not provided by the guest. Fill
4019 * in the host registers (via FXSAVE) instead, so they won't be modified.
4020 * (preemption has to stay disabled until FXRSTOR).
4021 *
4022 * Use noinline to keep the stack for other functions called by callers small.
4023 */
4024static noinline int fxregs_fixup(struct fxregs_state *fx_state,
4025 const size_t used_size)
4026{
4027 struct fxregs_state fx_tmp;
4028 int rc;
4029
4030 rc = asm_safe("fxsave %[fx]", , [fx] "+m"(fx_tmp));
4031 memcpy((void *)fx_state + used_size, (void *)&fx_tmp + used_size,
4032 __fxstate_size(16) - used_size);
4033
4034 return rc;
4035}
4036
4017static int em_fxrstor(struct x86_emulate_ctxt *ctxt) 4037static int em_fxrstor(struct x86_emulate_ctxt *ctxt)
4018{ 4038{
4019 struct fxregs_state fx_state; 4039 struct fxregs_state fx_state;
@@ -4024,19 +4044,19 @@ static int em_fxrstor(struct x86_emulate_ctxt *ctxt)
4024 if (rc != X86EMUL_CONTINUE) 4044 if (rc != X86EMUL_CONTINUE)
4025 return rc; 4045 return rc;
4026 4046
4047 size = fxstate_size(ctxt);
4048 rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state, size);
4049 if (rc != X86EMUL_CONTINUE)
4050 return rc;
4051
4027 ctxt->ops->get_fpu(ctxt); 4052 ctxt->ops->get_fpu(ctxt);
4028 4053
4029 size = fxstate_size(ctxt);
4030 if (size < __fxstate_size(16)) { 4054 if (size < __fxstate_size(16)) {
4031 rc = asm_safe("fxsave %[fx]", , [fx] "+m"(fx_state)); 4055 rc = fxregs_fixup(&fx_state, size);
4032 if (rc != X86EMUL_CONTINUE) 4056 if (rc != X86EMUL_CONTINUE)
4033 goto out; 4057 goto out;
4034 } 4058 }
4035 4059
4036 rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state, size);
4037 if (rc != X86EMUL_CONTINUE)
4038 goto out;
4039
4040 if (fx_state.mxcsr >> 16) { 4060 if (fx_state.mxcsr >> 16) {
4041 rc = emulate_gp(ctxt, 0); 4061 rc = emulate_gp(ctxt, 0);
4042 goto out; 4062 goto out;