From: "Jason A. Donenfeld" <Jason@zx2c4.com> To: "Michael S. Tsirkin" <mst@redhat.com> Cc: "Laszlo Ersek" <lersek@redhat.com>, LKML <linux-kernel@vger.kernel.org>, "KVM list" <kvm@vger.kernel.org>, "QEMU Developers" <qemu-devel@nongnu.org>, linux-hyperv@vger.kernel.org, "Linux Crypto Mailing List" <linux-crypto@vger.kernel.org>, "Alexander Graf" <graf@amazon.com>, "Michael Kelley (LINUX)" <mikelley@microsoft.com>, "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>, adrian@parity.io, "Daniel P. Berrangé" <berrange@redhat.com>, "Dominik Brodowski" <linux@dominikbrodowski.net>, "Jann Horn" <jannh@google.com>, "Rafael J. Wysocki" <rafael@kernel.org>, "Brown, Len" <len.brown@intel.com>, "Pavel Machek" <pavel@ucw.cz>, "Linux PM" <linux-pm@vger.kernel.org>, "Colm MacCarthaigh" <colmmacc@amazon.com>, "Theodore Ts'o" <tytso@mit.edu>, "Arnd Bergmann" <arnd@arndb.de> Subject: Re: propagating vmgenid outward and upward Date: Wed, 2 Mar 2022 16:36:49 +0100 [thread overview] Message-ID: <Yh+PET49oHNpxn+H@zx2c4.com> (raw) In-Reply-To: <20220302101602-mutt-send-email-mst@kernel.org> Hi Michael, On Wed, Mar 02, 2022 at 10:20:25AM -0500, Michael S. Tsirkin wrote: > So writing some code: > > 1: > put plaintext in a buffer > put a key in a buffer > put the nonce for that encryption in a buffer > > if vm gen id != stored vm gen id > stored vm gen id = vm gen id > goto 1 > > I think this is race free, but I don't see why does it matter whether we > read gen id atomically or not. Because that 16 byte read of vmgenid is not atomic. Let's say you read the first 8 bytes, and then the VM is forked. In the forked VM, the next 8 bytes are the same as last time, but the first 8 bytes, which you already read, have changed. In that case, your != becomes a ==, and the test fails. This is one of those fundamental things of "unique ID" vs "generation counter word". Anyway, per your request in your last email, I wrote some code for this, which may or may not be totally broken, and only works on 64-bit x86, which is really the best possible case in terms of performance. And even so, it's not great. Jason --------8<------------------------ diff --git a/drivers/net/wireguard/noise.c b/drivers/net/wireguard/noise.c index 720952b92e78..250b8973007d 100644 --- a/drivers/net/wireguard/noise.c +++ b/drivers/net/wireguard/noise.c @@ -106,6 +106,7 @@ static struct noise_keypair *keypair_create(struct wg_peer *peer) keypair->entry.type = INDEX_HASHTABLE_KEYPAIR; keypair->entry.peer = peer; kref_init(&keypair->refcount); + keypair->vmgenid = vmgenid_read_atomic(); return keypair; } diff --git a/drivers/net/wireguard/noise.h b/drivers/net/wireguard/noise.h index c527253dba80..0add240a14a0 100644 --- a/drivers/net/wireguard/noise.h +++ b/drivers/net/wireguard/noise.h @@ -27,10 +27,13 @@ struct noise_symmetric_key { bool is_valid; }; +extern __uint128_t vmgenid_read_atomic(void); + struct noise_keypair { struct index_hashtable_entry entry; struct noise_symmetric_key sending; atomic64_t sending_counter; + __uint128_t vmgenid; struct noise_symmetric_key receiving; struct noise_replay_counter receiving_counter; __le32 remote_index; diff --git a/drivers/net/wireguard/send.c b/drivers/net/wireguard/send.c index 5368f7c35b4b..40d016be59e3 100644 --- a/drivers/net/wireguard/send.c +++ b/drivers/net/wireguard/send.c @@ -381,6 +381,9 @@ void wg_packet_send_staged_packets(struct wg_peer *peer) goto out_invalid; } + if (keypair->vmgenid != vmgenid_read_atomic()) + goto out_invalid; + packets.prev->next = NULL; wg_peer_get(keypair->entry.peer); PACKET_CB(packets.next)->keypair = keypair; diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c index 0ae1a39f2e28..c122fae1d494 100644 --- a/drivers/virt/vmgenid.c +++ b/drivers/virt/vmgenid.c @@ -21,6 +21,21 @@ struct vmgenid_state { u8 this_id[VMGENID_SIZE]; }; +static __uint128_t *val; + +__uint128_t vmgenid_read_atomic(void) +{ + __uint128_t ret = 0; + if (!val) + return 0; + asm volatile("lock cmpxchg16b %1" + : "+A"(ret) + : "m"(*val), "b"(0), "c"(0) + : "cc"); + return ret; +} +EXPORT_SYMBOL(vmgenid_read_atomic); + static int vmgenid_add(struct acpi_device *device) { struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER }; @@ -50,6 +65,7 @@ static int vmgenid_add(struct acpi_device *device) phys_addr = (obj->package.elements[0].integer.value << 0) | (obj->package.elements[1].integer.value << 32); state->next_id = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB); + val = (__uint128_t *)state->next_id; if (IS_ERR(state->next_id)) { ret = PTR_ERR(state->next_id); goto out;
WARNING: multiple messages have this Message-ID (diff)
From: "Jason A. Donenfeld" <Jason@zx2c4.com> To: "Michael S. Tsirkin" <mst@redhat.com> Cc: "Brown, Len" <len.brown@intel.com>, linux-hyperv@vger.kernel.org, "Colm MacCarthaigh" <colmmacc@amazon.com>, "Daniel P. Berrangé" <berrange@redhat.com>, adrian@parity.io, "KVM list" <kvm@vger.kernel.org>, "Jann Horn" <jannh@google.com>, "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>, "Linux PM" <linux-pm@vger.kernel.org>, "Rafael J. Wysocki" <rafael@kernel.org>, LKML <linux-kernel@vger.kernel.org>, "Dominik Brodowski" <linux@dominikbrodowski.net>, "QEMU Developers" <qemu-devel@nongnu.org>, "Alexander Graf" <graf@amazon.com>, "Linux Crypto Mailing List" <linux-crypto@vger.kernel.org>, "Pavel Machek" <pavel@ucw.cz>, "Theodore Ts'o" <tytso@mit.edu>, "Michael Kelley (LINUX)" <mikelley@microsoft.com>, "Laszlo Ersek" <lersek@redhat.com>, "Arnd Bergmann" <arnd@arndb.de> Subject: Re: propagating vmgenid outward and upward Date: Wed, 2 Mar 2022 16:36:49 +0100 [thread overview] Message-ID: <Yh+PET49oHNpxn+H@zx2c4.com> (raw) In-Reply-To: <20220302101602-mutt-send-email-mst@kernel.org> Hi Michael, On Wed, Mar 02, 2022 at 10:20:25AM -0500, Michael S. Tsirkin wrote: > So writing some code: > > 1: > put plaintext in a buffer > put a key in a buffer > put the nonce for that encryption in a buffer > > if vm gen id != stored vm gen id > stored vm gen id = vm gen id > goto 1 > > I think this is race free, but I don't see why does it matter whether we > read gen id atomically or not. Because that 16 byte read of vmgenid is not atomic. Let's say you read the first 8 bytes, and then the VM is forked. In the forked VM, the next 8 bytes are the same as last time, but the first 8 bytes, which you already read, have changed. In that case, your != becomes a ==, and the test fails. This is one of those fundamental things of "unique ID" vs "generation counter word". Anyway, per your request in your last email, I wrote some code for this, which may or may not be totally broken, and only works on 64-bit x86, which is really the best possible case in terms of performance. And even so, it's not great. Jason --------8<------------------------ diff --git a/drivers/net/wireguard/noise.c b/drivers/net/wireguard/noise.c index 720952b92e78..250b8973007d 100644 --- a/drivers/net/wireguard/noise.c +++ b/drivers/net/wireguard/noise.c @@ -106,6 +106,7 @@ static struct noise_keypair *keypair_create(struct wg_peer *peer) keypair->entry.type = INDEX_HASHTABLE_KEYPAIR; keypair->entry.peer = peer; kref_init(&keypair->refcount); + keypair->vmgenid = vmgenid_read_atomic(); return keypair; } diff --git a/drivers/net/wireguard/noise.h b/drivers/net/wireguard/noise.h index c527253dba80..0add240a14a0 100644 --- a/drivers/net/wireguard/noise.h +++ b/drivers/net/wireguard/noise.h @@ -27,10 +27,13 @@ struct noise_symmetric_key { bool is_valid; }; +extern __uint128_t vmgenid_read_atomic(void); + struct noise_keypair { struct index_hashtable_entry entry; struct noise_symmetric_key sending; atomic64_t sending_counter; + __uint128_t vmgenid; struct noise_symmetric_key receiving; struct noise_replay_counter receiving_counter; __le32 remote_index; diff --git a/drivers/net/wireguard/send.c b/drivers/net/wireguard/send.c index 5368f7c35b4b..40d016be59e3 100644 --- a/drivers/net/wireguard/send.c +++ b/drivers/net/wireguard/send.c @@ -381,6 +381,9 @@ void wg_packet_send_staged_packets(struct wg_peer *peer) goto out_invalid; } + if (keypair->vmgenid != vmgenid_read_atomic()) + goto out_invalid; + packets.prev->next = NULL; wg_peer_get(keypair->entry.peer); PACKET_CB(packets.next)->keypair = keypair; diff --git a/drivers/virt/vmgenid.c b/drivers/virt/vmgenid.c index 0ae1a39f2e28..c122fae1d494 100644 --- a/drivers/virt/vmgenid.c +++ b/drivers/virt/vmgenid.c @@ -21,6 +21,21 @@ struct vmgenid_state { u8 this_id[VMGENID_SIZE]; }; +static __uint128_t *val; + +__uint128_t vmgenid_read_atomic(void) +{ + __uint128_t ret = 0; + if (!val) + return 0; + asm volatile("lock cmpxchg16b %1" + : "+A"(ret) + : "m"(*val), "b"(0), "c"(0) + : "cc"); + return ret; +} +EXPORT_SYMBOL(vmgenid_read_atomic); + static int vmgenid_add(struct acpi_device *device) { struct acpi_buffer parsed = { ACPI_ALLOCATE_BUFFER }; @@ -50,6 +65,7 @@ static int vmgenid_add(struct acpi_device *device) phys_addr = (obj->package.elements[0].integer.value << 0) | (obj->package.elements[1].integer.value << 32); state->next_id = devm_memremap(&device->dev, phys_addr, VMGENID_SIZE, MEMREMAP_WB); + val = (__uint128_t *)state->next_id; if (IS_ERR(state->next_id)) { ret = PTR_ERR(state->next_id); goto out;
next prev parent reply other threads:[~2022-03-02 15:37 UTC|newest] Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-03-01 15:42 propagating vmgenid outward and upward Jason A. Donenfeld 2022-03-01 16:15 ` Laszlo Ersek 2022-03-01 16:28 ` Jason A. Donenfeld 2022-03-01 16:28 ` Jason A. Donenfeld 2022-03-01 17:17 ` Michael S. Tsirkin 2022-03-01 17:17 ` Michael S. Tsirkin 2022-03-01 18:37 ` Jason A. Donenfeld 2022-03-01 18:37 ` Jason A. Donenfeld 2022-03-02 7:42 ` Michael S. Tsirkin 2022-03-02 7:42 ` Michael S. Tsirkin 2022-03-02 7:48 ` Michael S. Tsirkin 2022-03-02 7:48 ` Michael S. Tsirkin 2022-03-02 8:30 ` Michael S. Tsirkin 2022-03-02 8:30 ` Michael S. Tsirkin 2022-03-02 11:26 ` Jason A. Donenfeld 2022-03-02 11:26 ` Jason A. Donenfeld 2022-03-02 12:58 ` Michael S. Tsirkin 2022-03-02 12:58 ` Michael S. Tsirkin 2022-03-02 13:55 ` Jason A. Donenfeld 2022-03-02 13:55 ` Jason A. Donenfeld 2022-03-02 14:46 ` Michael S. Tsirkin 2022-03-02 14:46 ` Michael S. Tsirkin 2022-03-02 15:14 ` Jason A. Donenfeld 2022-03-02 15:14 ` Jason A. Donenfeld 2022-03-02 15:20 ` Michael S. Tsirkin 2022-03-02 15:20 ` Michael S. Tsirkin 2022-03-02 15:36 ` Jason A. Donenfeld [this message] 2022-03-02 15:36 ` Jason A. Donenfeld 2022-03-02 16:22 ` Michael S. Tsirkin 2022-03-02 16:22 ` Michael S. Tsirkin 2022-03-02 16:32 ` Jason A. Donenfeld 2022-03-02 16:32 ` Jason A. Donenfeld 2022-03-02 17:27 ` Michael S. Tsirkin 2022-03-02 17:27 ` Michael S. Tsirkin 2022-03-03 13:07 ` Michael S. Tsirkin 2022-03-03 13:07 ` Michael S. Tsirkin 2022-03-02 16:29 ` Michael S. Tsirkin 2022-03-02 16:29 ` Michael S. Tsirkin 2022-03-01 16:21 ` Michael S. Tsirkin 2022-03-01 16:21 ` Michael S. Tsirkin 2022-03-01 16:35 ` Jason A. Donenfeld 2022-03-01 16:35 ` Jason A. Donenfeld 2022-03-01 18:01 ` Greg KH 2022-03-01 18:01 ` Greg KH 2022-03-01 18:24 ` Jason A. Donenfeld 2022-03-01 18:24 ` Jason A. Donenfeld 2022-03-01 19:41 ` Greg KH 2022-03-01 19:41 ` Greg KH 2022-03-01 23:12 ` Jason A. Donenfeld 2022-03-01 23:12 ` Jason A. Donenfeld 2022-03-02 14:35 ` Jason A. Donenfeld 2022-03-09 10:10 ` Alexander Graf 2022-03-09 22:02 ` Jason A. Donenfeld 2022-03-09 22:02 ` Jason A. Donenfeld 2022-03-10 11:18 ` Alexander Graf 2022-03-20 22:53 ` Michael S. Tsirkin 2022-03-20 22:53 ` Michael S. Tsirkin 2022-04-19 15:12 ` Jason A. Donenfeld 2022-04-19 15:12 ` Jason A. Donenfeld 2022-04-19 16:43 ` Michael S. Tsirkin 2022-04-19 16:43 ` Michael S. Tsirkin
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