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Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
Cross-merge networking fixes after downstream PR. No conflicts. Adjacent changes: drivers/net/ethernet/intel/igc/igc_main.c 06b4125 ("igc: Add lock to safeguard global Qbv variables") d375007 ("igc: Add TransmissionOverrun counter") drivers/net/ethernet/microsoft/mana/mana_en.c a7dfeda ("net: mana: Fix MANA VF unload when hardware is unresponsive") a9ca9f9 ("page_pool: split types and declarations from page_pool.h") 92272ec ("eth: add missing xdp.h includes in drivers") net/mptcp/protocol.h 511b90e ("mptcp: fix disconnect vs accept race") b8dc6d6 ("mptcp: fix rcv buffer auto-tuning") tools/testing/selftests/net/mptcp/mptcp_join.sh c8c101a ("selftests: mptcp: join: fix 'implicit EP' test") 03668c6 ("selftests: mptcp: join: rework detailed report") Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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Documentation/admin-guide/hw-vuln/gather_data_sampling.rst
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| .. SPDX-License-Identifier: GPL-2.0 | ||
| GDS - Gather Data Sampling | ||
| ========================== | ||
|
|
||
| Gather Data Sampling is a hardware vulnerability which allows unprivileged | ||
| speculative access to data which was previously stored in vector registers. | ||
|
|
||
| Problem | ||
| ------- | ||
| When a gather instruction performs loads from memory, different data elements | ||
| are merged into the destination vector register. However, when a gather | ||
| instruction that is transiently executed encounters a fault, stale data from | ||
| architectural or internal vector registers may get transiently forwarded to the | ||
| destination vector register instead. This will allow a malicious attacker to | ||
| infer stale data using typical side channel techniques like cache timing | ||
| attacks. GDS is a purely sampling-based attack. | ||
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| The attacker uses gather instructions to infer the stale vector register data. | ||
| The victim does not need to do anything special other than use the vector | ||
| registers. The victim does not need to use gather instructions to be | ||
| vulnerable. | ||
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| Because the buffers are shared between Hyper-Threads cross Hyper-Thread attacks | ||
| are possible. | ||
|
|
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| Attack scenarios | ||
| ---------------- | ||
| Without mitigation, GDS can infer stale data across virtually all | ||
| permission boundaries: | ||
|
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| Non-enclaves can infer SGX enclave data | ||
| Userspace can infer kernel data | ||
| Guests can infer data from hosts | ||
| Guest can infer guest from other guests | ||
| Users can infer data from other users | ||
|
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| Because of this, it is important to ensure that the mitigation stays enabled in | ||
| lower-privilege contexts like guests and when running outside SGX enclaves. | ||
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| The hardware enforces the mitigation for SGX. Likewise, VMMs should ensure | ||
| that guests are not allowed to disable the GDS mitigation. If a host erred and | ||
| allowed this, a guest could theoretically disable GDS mitigation, mount an | ||
| attack, and re-enable it. | ||
|
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| Mitigation mechanism | ||
| -------------------- | ||
| This issue is mitigated in microcode. The microcode defines the following new | ||
| bits: | ||
|
|
||
| ================================ === ============================ | ||
| IA32_ARCH_CAPABILITIES[GDS_CTRL] R/O Enumerates GDS vulnerability | ||
| and mitigation support. | ||
| IA32_ARCH_CAPABILITIES[GDS_NO] R/O Processor is not vulnerable. | ||
| IA32_MCU_OPT_CTRL[GDS_MITG_DIS] R/W Disables the mitigation | ||
| 0 by default. | ||
| IA32_MCU_OPT_CTRL[GDS_MITG_LOCK] R/W Locks GDS_MITG_DIS=0. Writes | ||
| to GDS_MITG_DIS are ignored | ||
| Can't be cleared once set. | ||
| ================================ === ============================ | ||
|
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| GDS can also be mitigated on systems that don't have updated microcode by | ||
| disabling AVX. This can be done by setting gather_data_sampling="force" or | ||
| "clearcpuid=avx" on the kernel command-line. | ||
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| If used, these options will disable AVX use by turning off XSAVE YMM support. | ||
| However, the processor will still enumerate AVX support. Userspace that | ||
| does not follow proper AVX enumeration to check both AVX *and* XSAVE YMM | ||
| support will break. | ||
|
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||
| Mitigation control on the kernel command line | ||
| --------------------------------------------- | ||
| The mitigation can be disabled by setting "gather_data_sampling=off" or | ||
| "mitigations=off" on the kernel command line. Not specifying either will default | ||
| to the mitigation being enabled. Specifying "gather_data_sampling=force" will | ||
| use the microcode mitigation when available or disable AVX on affected systems | ||
| where the microcode hasn't been updated to include the mitigation. | ||
|
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| GDS System Information | ||
| ------------------------ | ||
| The kernel provides vulnerability status information through sysfs. For | ||
| GDS this can be accessed by the following sysfs file: | ||
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| /sys/devices/system/cpu/vulnerabilities/gather_data_sampling | ||
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| The possible values contained in this file are: | ||
|
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||
| ============================== ============================================= | ||
| Not affected Processor not vulnerable. | ||
| Vulnerable Processor vulnerable and mitigation disabled. | ||
| Vulnerable: No microcode Processor vulnerable and microcode is missing | ||
| mitigation. | ||
| Mitigation: AVX disabled, | ||
| no microcode Processor is vulnerable and microcode is missing | ||
| mitigation. AVX disabled as mitigation. | ||
| Mitigation: Microcode Processor is vulnerable and mitigation is in | ||
| effect. | ||
| Mitigation: Microcode (locked) Processor is vulnerable and mitigation is in | ||
| effect and cannot be disabled. | ||
| Unknown: Dependent on | ||
| hypervisor status Running on a virtual guest processor that is | ||
| affected but with no way to know if host | ||
| processor is mitigated or vulnerable. | ||
| ============================== ============================================= | ||
|
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||
| GDS Default mitigation | ||
| ---------------------- | ||
| The updated microcode will enable the mitigation by default. The kernel's | ||
| default action is to leave the mitigation enabled. |
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