| Message ID | b8723d39903b64c241c50f5513f804390c7b5eec.1718203311.git.babu.moger@amd.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] KVM: Fix Undefined Behavior Sanitizer(UBSAN) error | expand |
On Wed, 12 Jun 2024 09:41:51 -0500, Babu Moger wrote: > System throws this following UBSAN: invalid-load error when the very first > VM is powered up on a freshly booted host machine. Happens only with 2P or > 4P (multiple sockets) systems. > > { 688.429145] ------------[ cut here ]------------ > [ 688.429156] UBSAN: invalid-load in arch/x86/kvm/../../../virt/kvm/kvm_main.c:655:10 > [ 688.437739] load of value 160 is not a valid value for type '_Bool' > [ 688.444760] CPU: 370 PID: 8246 Comm: CPU 0/KVM Not tainted 6.8.2-amdsos-build58-ubuntu-22.04+ #1 > [ 688.444767] Hardware name: AMD Corporation Sh54p/Sh54p, BIOS WPC4429N 04/25/2024 > [ 688.444770] Call Trace: > [ 688.444777] <TASK> > [ 688.444787] dump_stack_lvl+0x48/0x60 > [ 688.444810] ubsan_epilogue+0x5/0x30 > [ 688.444823] __ubsan_handle_load_invalid_value+0x79/0x80 > [ 688.444827] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.444836] ? flush_tlb_func+0xe9/0x2e0 > [ 688.444845] kvm_mmu_notifier_invalidate_range_end.cold+0x18/0x4f [kvm] > [ 688.444906] __mmu_notifier_invalidate_range_end+0x63/0xe0 > [ 688.444917] __split_huge_pmd+0x367/0xfc0 > [ 688.444928] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.444931] ? alloc_pages_mpol+0x97/0x210 > [ 688.444941] do_huge_pmd_wp_page+0x1cc/0x380 > [ 688.444946] __handle_mm_fault+0x8ee/0xe50 > [ 688.444958] handle_mm_fault+0xe4/0x4a0 > [ 688.444962] __get_user_pages+0x190/0x840 > [ 688.444972] get_user_pages_unlocked+0xe0/0x590 > [ 688.444977] hva_to_pfn+0x114/0x550 [kvm] > [ 688.445007] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445011] ? __gfn_to_pfn_memslot+0x3b/0xd0 [kvm] > [ 688.445037] kvm_faultin_pfn+0xed/0x5b0 [kvm] > [ 688.445079] kvm_tdp_page_fault+0x123/0x170 [kvm] > [ 688.445109] kvm_mmu_page_fault+0x244/0xaa0 [kvm] > [ 688.445136] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445138] ? kvm_io_bus_get_first_dev+0x56/0xf0 [kvm] > [ 688.445165] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445171] ? svm_vcpu_run+0x329/0x7c0 [kvm_amd] > [ 688.445186] vcpu_enter_guest+0x592/0x1070 [kvm] > [ 688.445223] kvm_arch_vcpu_ioctl_run+0x145/0x8a0 [kvm] > [ 688.445254] kvm_vcpu_ioctl+0x288/0x6d0 [kvm] > [ 688.445279] ? vcpu_put+0x22/0x50 [kvm] > [ 688.445305] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445307] ? kvm_arch_vcpu_ioctl_run+0x346/0x8a0 [kvm] > [ 688.445335] __x64_sys_ioctl+0x8f/0xd0 > [ 688.445343] do_syscall_64+0x77/0x120 > [ 688.445353] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445355] ? fire_user_return_notifiers+0x42/0x70 > [ 688.445363] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445365] ? syscall_exit_to_user_mode+0x82/0x1b0 > [ 688.445372] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445377] ? do_syscall_64+0x86/0x120 > [ 688.445380] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445383] ? do_syscall_64+0x86/0x120 > [ 688.445388] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445392] ? do_syscall_64+0x86/0x120 > [ 688.445396] ? srso_alias_return_thunk+0x5/0xfbef5 > [ 688.445400] ? do_syscall_64+0x86/0x120 > [ 688.445404] ? do_syscall_64+0x86/0x120 > [ 688.445407] ? do_syscall_64+0x86/0x120 > [ 688.445410] entry_SYSCALL_64_after_hwframe+0x6e/0x76 > [ 688.445416] RIP: 0033:0x7fdf2ed1a94f > [ 688.445421] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 > 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <41> > 89 c0 3d 00 f0 ff ff 77 1f 48 8b 44 24 18 64 48 2b 04 25 28 00 > [ 688.445424] RSP: 002b:00007fc127bff460 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > [ 688.445429] RAX: ffffffffffffffda RBX: 000000000000ae80 RCX: 00007fdf2ed1a94f > [ 688.445432] RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000016 > [ 688.445434] RBP: 00005586f80dc350 R08: 00005586f6a0af10 R09: 00000000ffffffff > [ 688.445436] R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000 > [ 688.445438] R13: 0000000000000001 R14: 0000000000000cf8 R15: 0000000000000000 > [ 688.445443] </TASK> > [ 688.445444] ---[ end trace ]--- Please trim splats like this, the timestamps are uninteresting, and in most cases, the "? ..." lines are completely superfluous. The changelog+shortlog should also focus on what the actual bug+fix is. The fact that UBSAN found the issue is definitely noteworthy, but it's secondary to describing the actual bug. Lastly, it's definitely worth calling out that the bug is benign in practice. kvm_mmu_notifier_invalidate_range_end() is the only caller that passes a null handler, and it has flush_on_ret=false, i.e. won't actually consume whatever garbage ends up in r.ret. Not to mention that the compiler elides the entire sequence on every build I've looked at, even an UBSAN=y builds, i.e. it likely takes a sanitizer-heavy kernel to actually generate code that yields undefined behavior at runtime. KVM: Stop processing *all* memslots when "null" mmu_notifier handler is found Bail from outer address space loop, not just the inner memslot loop, when a "null" handler is encountered by __kvm_handle_hva_range(), which is the intended behavior. On x86, which has multiple address spaces thanks to SMM emulation, breaking from just the memslot loop results in undefined behavior due to assigning the non-existent return value from kvm_null_fn() to a bool. In practice, the bug is benign as kvm_mmu_notifier_invalidate_range_end() is the only caller that passes handler=kvm_null_fn, and it doesn't set flush_on_ret, i.e. assigning garbage to r.ret is ultimately ignored. And for most configuration the compiler elides the entire sequence, i.e. there is no undefined behavior at runtime. ------------[ cut here ]------------ UBSAN: invalid-load in arch/x86/kvm/../../../virt/kvm/kvm_main.c:655:10 load of value 160 is not a valid value for type '_Bool' CPU: 370 PID: 8246 Comm: CPU 0/KVM Not tainted 6.8.2-amdsos-build58-ubuntu-22.04+ #1 Hardware name: AMD Corporation Sh54p/Sh54p, BIOS WPC4429N 04/25/2024 Call Trace: <TASK> dump_stack_lvl+0x48/0x60 ubsan_epilogue+0x5/0x30 __ubsan_handle_load_invalid_value+0x79/0x80 kvm_mmu_notifier_invalidate_range_end.cold+0x18/0x4f [kvm] __mmu_notifier_invalidate_range_end+0x63/0xe0 __split_huge_pmd+0x367/0xfc0 do_huge_pmd_wp_page+0x1cc/0x380 __handle_mm_fault+0x8ee/0xe50 handle_mm_fault+0xe4/0x4a0 __get_user_pages+0x190/0x840 get_user_pages_unlocked+0xe0/0x590 hva_to_pfn+0x114/0x550 [kvm] kvm_faultin_pfn+0xed/0x5b0 [kvm] kvm_tdp_page_fault+0x123/0x170 [kvm] kvm_mmu_page_fault+0x244/0xaa0 [kvm] vcpu_enter_guest+0x592/0x1070 [kvm] kvm_arch_vcpu_ioctl_run+0x145/0x8a0 [kvm] kvm_vcpu_ioctl+0x288/0x6d0 [kvm] __x64_sys_ioctl+0x8f/0xd0 do_syscall_64+0x77/0x120 entry_SYSCALL_64_after_hwframe+0x6e/0x76 </TASK> ---[ end trace ]--- Fixes: 071064f14d87 ("KVM: Don't take mmu_lock for range invalidation unless necessary") Signed-off-by: Babu Moger <babu.moger@amd.com> Link: https://lore.kernel.org/r/b8723d39903b64c241c50f5513f804390c7b5eec.1718203311.git.babu.moger@amd.com [sean: massage changelog] Signed-off-by: Sean Christopherson <seanjc@google.com> Applied to kvm-x86 fixes, with the above shortlog+changelog (I am planning on send a pull request to Paolo for a few 6.10 fixes on Thursday). Thanks! [1/1] KVM: Stop processing *all* memslots when "null" mmu_notifier handler is found https://github.com/kvm-x86/linux/commit/201de7ec31e5 -- https://github.com/kvm-x86/linux/tree/next
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 14841acb8b95..d65d3aa99650 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -651,7 +651,7 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, range->on_lock(kvm); if (IS_KVM_NULL_FN(range->handler)) - break; + goto mmu_unlock; } r.ret |= range->handler(kvm, &gfn_range); } @@ -660,6 +660,7 @@ static __always_inline kvm_mn_ret_t __kvm_handle_hva_range(struct kvm *kvm, if (range->flush_on_ret && r.ret) kvm_flush_remote_tlbs(kvm); +mmu_unlock: if (r.found_memslot) KVM_MMU_UNLOCK(kvm);
System throws this following UBSAN: invalid-load error when the very first VM is powered up on a freshly booted host machine. Happens only with 2P or 4P (multiple sockets) systems. { 688.429145] ------------[ cut here ]------------ [ 688.429156] UBSAN: invalid-load in arch/x86/kvm/../../../virt/kvm/kvm_main.c:655:10 [ 688.437739] load of value 160 is not a valid value for type '_Bool' [ 688.444760] CPU: 370 PID: 8246 Comm: CPU 0/KVM Not tainted 6.8.2-amdsos-build58-ubuntu-22.04+ #1 [ 688.444767] Hardware name: AMD Corporation Sh54p/Sh54p, BIOS WPC4429N 04/25/2024 [ 688.444770] Call Trace: [ 688.444777] <TASK> [ 688.444787] dump_stack_lvl+0x48/0x60 [ 688.444810] ubsan_epilogue+0x5/0x30 [ 688.444823] __ubsan_handle_load_invalid_value+0x79/0x80 [ 688.444827] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.444836] ? flush_tlb_func+0xe9/0x2e0 [ 688.444845] kvm_mmu_notifier_invalidate_range_end.cold+0x18/0x4f [kvm] [ 688.444906] __mmu_notifier_invalidate_range_end+0x63/0xe0 [ 688.444917] __split_huge_pmd+0x367/0xfc0 [ 688.444928] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.444931] ? alloc_pages_mpol+0x97/0x210 [ 688.444941] do_huge_pmd_wp_page+0x1cc/0x380 [ 688.444946] __handle_mm_fault+0x8ee/0xe50 [ 688.444958] handle_mm_fault+0xe4/0x4a0 [ 688.444962] __get_user_pages+0x190/0x840 [ 688.444972] get_user_pages_unlocked+0xe0/0x590 [ 688.444977] hva_to_pfn+0x114/0x550 [kvm] [ 688.445007] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445011] ? __gfn_to_pfn_memslot+0x3b/0xd0 [kvm] [ 688.445037] kvm_faultin_pfn+0xed/0x5b0 [kvm] [ 688.445079] kvm_tdp_page_fault+0x123/0x170 [kvm] [ 688.445109] kvm_mmu_page_fault+0x244/0xaa0 [kvm] [ 688.445136] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445138] ? kvm_io_bus_get_first_dev+0x56/0xf0 [kvm] [ 688.445165] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445171] ? svm_vcpu_run+0x329/0x7c0 [kvm_amd] [ 688.445186] vcpu_enter_guest+0x592/0x1070 [kvm] [ 688.445223] kvm_arch_vcpu_ioctl_run+0x145/0x8a0 [kvm] [ 688.445254] kvm_vcpu_ioctl+0x288/0x6d0 [kvm] [ 688.445279] ? vcpu_put+0x22/0x50 [kvm] [ 688.445305] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445307] ? kvm_arch_vcpu_ioctl_run+0x346/0x8a0 [kvm] [ 688.445335] __x64_sys_ioctl+0x8f/0xd0 [ 688.445343] do_syscall_64+0x77/0x120 [ 688.445353] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445355] ? fire_user_return_notifiers+0x42/0x70 [ 688.445363] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445365] ? syscall_exit_to_user_mode+0x82/0x1b0 [ 688.445372] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445377] ? do_syscall_64+0x86/0x120 [ 688.445380] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445383] ? do_syscall_64+0x86/0x120 [ 688.445388] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445392] ? do_syscall_64+0x86/0x120 [ 688.445396] ? srso_alias_return_thunk+0x5/0xfbef5 [ 688.445400] ? do_syscall_64+0x86/0x120 [ 688.445404] ? do_syscall_64+0x86/0x120 [ 688.445407] ? do_syscall_64+0x86/0x120 [ 688.445410] entry_SYSCALL_64_after_hwframe+0x6e/0x76 [ 688.445416] RIP: 0033:0x7fdf2ed1a94f [ 688.445421] Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <41> 89 c0 3d 00 f0 ff ff 77 1f 48 8b 44 24 18 64 48 2b 04 25 28 00 [ 688.445424] RSP: 002b:00007fc127bff460 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 688.445429] RAX: ffffffffffffffda RBX: 000000000000ae80 RCX: 00007fdf2ed1a94f [ 688.445432] RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000016 [ 688.445434] RBP: 00005586f80dc350 R08: 00005586f6a0af10 R09: 00000000ffffffff [ 688.445436] R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000 [ 688.445438] R13: 0000000000000001 R14: 0000000000000cf8 R15: 0000000000000000 [ 688.445443] </TASK> [ 688.445444] ---[ end trace ]--- However, VM boots up fine without any issues and operational. The error is due to invalid assignment in kvm invalidate range end path. There is no arch specific handler for this case and handler is assigned to kvm_null_fn(). This is an empty function and returns void. Return value of this function is assigned to boolean variable. UBSAN complains about this incompatible assignment when kernel is compiled with CONFIG_UBSAN. Fix the issue by breaking out of memslot loop when the handler is null. Signed-off-by: Babu Moger <babu.moger@amd.com> Signed-off-by: Sean Christopherson <seanjc@google.com> --- v2: Updated with Sean's patch. Added his sign-off-by. --- virt/kvm/kvm_main.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)