kernel.git/arch/x86/kernel/cpu/common.c, branch linux-6.4.y

x86/speculation: Mark all Skylake CPUs as vulnerable to GDS

2023-09-13T07:48:34Z

[ Upstream commit c9f4c45c8ec3f07f4f083f9750032a1ec3eab6b2 ] The Gather Data Sampling (GDS) vulnerability is common to all Skylake processors. However, the "client" Skylakes* are now in this list: https://www.intel.com/content/www/us/en/support/articles/000022396/processors.html which means they are no longer included for new vulnerabilities here: https://www.intel.com/content/www/us/en/developer/topic-technology/software-security-guidance/processors-affected-consolidated-product-cpu-model.html or in other GDS documentation. Thus, they were not included in the original GDS mitigation patches. Mark SKYLAKE and SKYLAKE_L as vulnerable to GDS to match all the other Skylake CPUs (which include Kaby Lake). Also group the CPUs so that the ones that share the exact same vulnerabilities are next to each other. Last, move SRBDS to the end of each line. This makes it clear at a glance that SKYLAKE_X is unique. Of the five Skylakes, it is the only "server" CPU and has a different implementation from the clients of the "special register" hardware, making it immune to SRBDS. This makes the diff much harder to read, but the resulting table is worth it. I very much appreciate the report from Michael Zhivich about this issue. Despite what level of support a hardware vendor is providing, the kernel very much needs an accurate and up-to-date list of vulnerable CPUs. More reports like this are very welcome. * Client Skylakes are CPUID 406E3/506E3 which is family 6, models 0x4E and 0x5E, aka INTEL_FAM6_SKYLAKE and INTEL_FAM6_SKYLAKE_L. Reported-by: Michael Zhivich Fixes: 8974eb588283 ("x86/speculation: Add Gather Data Sampling mitigation") Signed-off-by: Dave Hansen Signed-off-by: Ingo Molnar Reviewed-by: Daniel Sneddon Cc: Linus Torvalds Signed-off-by: Sasha Levin

x86: fix backwards merge of GDS/SRSO bit

2023-08-08T18:04:53Z

Stable-tree-only change. Due to the way the GDS and SRSO patches flowed into the stable tree, it was a 50% chance that the merge of the which value GDS and SRSO should be. Of course, I lost that bet, and chose the opposite of what Linus chose in commit 64094e7e3118 ("Merge tag 'gds-for-linus-2023-08-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip") Fix this up by switching the values to match what is now in Linus's tree as that is the correct value to mirror. Signed-off-by: Greg Kroah-Hartman

x86/srso: Add SRSO_NO support

2023-08-08T18:04:52Z

Upstream commit: 1b5277c0ea0b247393a9c426769fde18cff5e2f6 Add support for the CPUID flag which denotes that the CPU is not affected by SRSO. Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Greg Kroah-Hartman

x86/srso: Add a Speculative RAS Overflow mitigation

2023-08-08T18:04:51Z

Upstream commit: fb3bd914b3ec28f5fb697ac55c4846ac2d542855 Add a mitigation for the speculative return address stack overflow vulnerability found on AMD processors. The mitigation works by ensuring all RET instructions speculate to a controlled location, similar to how speculation is controlled in the retpoline sequence. To accomplish this, the __x86_return_thunk forces the CPU to mispredict every function return using a 'safe return' sequence. To ensure the safety of this mitigation, the kernel must ensure that the safe return sequence is itself free from attacker interference. In Zen3 and Zen4, this is accomplished by creating a BTB alias between the untraining function srso_untrain_ret_alias() and the safe return function srso_safe_ret_alias() which results in evicting a potentially poisoned BTB entry and using that safe one for all function returns. In older Zen1 and Zen2, this is accomplished using a reinterpretation technique similar to Retbleed one: srso_untrain_ret() and srso_safe_ret(). Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Greg Kroah-Hartman

x86/speculation: Add Gather Data Sampling mitigation

2023-08-08T18:04:50Z

commit 8974eb588283b7d44a7c91fa09fcbaf380339f3a upstream Gather Data Sampling (GDS) is a hardware vulnerability which allows unprivileged speculative access to data which was previously stored in vector registers. Intel processors that support AVX2 and AVX512 have gather instructions that fetch non-contiguous data elements from memory. On vulnerable hardware, when a gather instruction is transiently executed and encounters a fault, stale data from architectural or internal vector registers may get transiently stored to the destination vector register allowing an attacker to infer the stale data using typical side channel techniques like cache timing attacks. This mitigation is different from many earlier ones for two reasons. First, it is enabled by default and a bit must be set to *DISABLE* it. This is the opposite of normal mitigation polarity. This means GDS can be mitigated simply by updating microcode and leaving the new control bit alone. Second, GDS has a "lock" bit. This lock bit is there because the mitigation affects the hardware security features KeyLocker and SGX. It needs to be enabled and *STAY* enabled for these features to be mitigated against GDS. The mitigation is enabled in the microcode by default. Disable it by setting gather_data_sampling=off or by disabling all mitigations with mitigations=off. The mitigation status can be checked by reading: /sys/devices/system/cpu/vulnerabilities/gather_data_sampling Signed-off-by: Daniel Sneddon Signed-off-by: Dave Hansen Acked-by: Josh Poimboeuf Signed-off-by: Daniel Sneddon Signed-off-by: Greg Kroah-Hartman

x86/fpu: Move FPU initialization into arch_cpu_finalize_init()

2023-08-08T18:04:50Z

commit b81fac906a8f9e682e513ddd95697ec7a20878d4 upstream Initializing the FPU during the early boot process is a pointless exercise. Early boot is convoluted and fragile enough. Nothing requires that the FPU is set up early. It has to be initialized before fork_init() because the task_struct size depends on the FPU register buffer size. Move the initialization to arch_cpu_finalize_init() which is the perfect place to do so. No functional change. This allows to remove quite some of the custom early command line parsing, but that's subject to the next installment. Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230613224545.902376621@linutronix.de Signed-off-by: Daniel Sneddon Signed-off-by: Greg Kroah-Hartman

x86/fpu: Remove cpuinfo argument from init functions

2023-08-08T18:04:50Z

commit 1f34bb2a24643e0087652d81078e4f616562738d upstream Nothing in the call chain requires it Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230613224545.783704297@linutronix.de Signed-off-by: Daniel Sneddon Signed-off-by: Greg Kroah-Hartman

x86/init: Initialize signal frame size late

2023-08-08T18:04:49Z

commit 54d9a91a3d6713d1332e93be13b4eaf0fa54349d upstream No point in doing this during really early boot. Move it to an early initcall so that it is set up before possible user mode helpers are started during device initialization. Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230613224545.727330699@linutronix.de Signed-off-by: Daniel Sneddon Signed-off-by: Greg Kroah-Hartman

init, x86: Move mem_encrypt_init() into arch_cpu_finalize_init()

2023-08-08T18:04:49Z

commit 439e17576eb47f26b78c5bbc72e344d4206d2327 upstream Invoke the X86ism mem_encrypt_init() from X86 arch_cpu_finalize_init() and remove the weak fallback from the core code. No functional change. Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20230613224545.670360645@linutronix.de Signed-off-by: Daniel Sneddon Signed-off-by: Greg Kroah-Hartman

x86/cpu: Switch to arch_cpu_finalize_init()

2023-08-08T18:04:48Z

commit 7c7077a72674402654f3291354720cd73cdf649e upstream check_bugs() is a dumping ground for finalizing the CPU bringup. Only parts of it has to do with actual CPU bugs. Split it apart into arch_cpu_finalize_init() and cpu_select_mitigations(). Fixup the bogus 32bit comments while at it. No functional change. Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20230613224545.019583869@linutronix.de Signed-off-by: Daniel Sneddon Signed-off-by: Greg Kroah-Hartman