On 31.10.2017 12:34, syzbot wrote: > Hello, > > syzkaller hit the following crash on > 91dfed74eabcdae9378131546c446442c29bf769 > git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master > compiler: gcc (GCC) 7.1.1 20170620 > .config is attached > Raw console output is attached. > C reproducer is attached > syzkaller reproducer is attached. See https://goo.gl/kgGztJ > for information about syzkaller reproducers > > > 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 > #1 > 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 In em_fxrstor, we do a get_fpu(), which in return disables preemption. With preempt_disable(), we do a segmented_read_std()->kvm_vcpu_read_guest_page(), triggering the warning. > 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 I don't really see a way to avoid two fxstate variables. Unloading the fpu in between the fxstore/fxrstr could lead to host values getting overwritten. Loading/saving the fpu in kvm_arch_vcpu_ioctl_run() would most probably also not work, as the relevant portions of fxregs_state would not get saved/restored. So the preemption would still be needed. So all I can offer for now is the following (untested, can send as proper patch if needed): >From f32d06c8c621c6d68e073e9bdb81a6280b6c9544 Mon Sep 17 00:00:00 2001 From: David Hildenbrand <david@xxxxxxxxxx> Date: Mon, 6 Nov 2017 12:35:39 +0100 Subject: [PATCH v1] KVM: x86: fix em_fxstor sleeping while in atomic Commit 9d643f63128b tried to optimize the stack size, but introduced a guest memory access which might sleep while in atomic. Let's undo that part of the commit but keep the cleanups. 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@xxxxxxxxxx> --- arch/x86/kvm/emulate.c | 16 +++++++++------- 1 file changed, 9 insertions(+), 7 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index fb0055953fbc..d87f01a2d6f4 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4002,7 +4002,7 @@ static int em_fxsave(struct x86_emulate_ctxt *ctxt) static int em_fxrstor(struct x86_emulate_ctxt *ctxt) { - struct fxregs_state fx_state; + struct fxregs_state fx_state, fx_old; int rc; size_t size; @@ -4010,19 +4010,21 @@ static int em_fxrstor(struct x86_emulate_ctxt *ctxt) if (rc != X86EMUL_CONTINUE) return rc; + size = fxstate_size(ctxt); + rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state, size); + if (rc != X86EMUL_CONTINUE) + return rc; + ctxt->ops->get_fpu(ctxt); - size = fxstate_size(ctxt); if (size < __fxstate_size(16)) { - rc = asm_safe("fxsave %[fx]", , [fx] "+m"(fx_state)); + rc = asm_safe("fxsave %[fx]", , [fx] "+m"(fx_old)); if (rc != X86EMUL_CONTINUE) goto out; + memcpy(((void *)&fx_state) + size, ((void *)&fx_old) + size, + __fxstate_size(16) - size); } - rc = segmented_read_std(ctxt, ctxt->memop.addr.mem, &fx_state, size); - if (rc != X86EMUL_CONTINUE) - goto out; - if (fx_state.mxcsr >> 16) { rc = emulate_gp(ctxt, 0); goto out; -- 2.13.6 -- Thanks, David / dhildenb
