kernel/linux.git/tools/arch/x86/include, branch v5.15.208

x86/CPU/AMD: Prevent improper isolation of shared resources in Zen2's op cache

2026-05-15T12:48:45+00:00

commit c21b90f77687075115d989e53a8ec5e2bb427ab1 upstream. Make sure resources are not improperly shared in the op cache and cause instruction corruption this way. Signed-off-by: Prathyushi Nangia Co-developed-by: Borislav Petkov (AMD) Signed-off-by: Borislav Petkov (AMD) Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman

x86/CPU/AMD: Add X86_FEATURE_ZEN1

2026-05-15T12:48:45+00:00

Commit 232afb557835d6f6859c73bf610bad308c96b131 upstream. Add a synthetic feature flag specifically for first generation Zen machines. There's need to have a generic flag for all Zen generations so make X86_FEATURE_ZEN be that flag. Fixes: 30fa92832f40 ("x86/CPU/AMD: Add ZenX generations flags") Suggested-by: Brian Gerst Suggested-by: Tom Lendacky Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/dc3835e3-0731-4230-bbb9-336bbe3d042b@amd.com Signed-off-by: Greg Kroah-Hartman

x86/bugs: Increase the x86 bugs vector size to two u32s

2023-08-08T17:58:33+00:00

Upstream commit: 0e52740ffd10c6c316837c6c128f460f1aaba1ea There was never a doubt in my mind that they would not fit into a single u32 eventually. Signed-off-by: Borislav Petkov (AMD) Signed-off-by: Greg Kroah-Hartman

x86/cpu: Restore AMD's DE_CFG MSR after resume

2022-11-16T08:58:31+00:00

commit 2632daebafd04746b4b96c2f26a6021bc38f6209 upstream. DE_CFG contains the LFENCE serializing bit, restore it on resume too. This is relevant to older families due to the way how they do S3. Unify and correct naming while at it. Fixes: e4d0e84e4907 ("x86/cpu/AMD: Make LFENCE a serializing instruction") Reported-by: Andrew Cooper Reported-by: Pawan Gupta Signed-off-by: Borislav Petkov Cc: Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

x86/speculation: Add RSB VM Exit protections

2022-08-11T11:07:54+00:00

commit 2b1299322016731d56807aa49254a5ea3080b6b3 upstream. tl;dr: The Enhanced IBRS mitigation for Spectre v2 does not work as documented for RET instructions after VM exits. Mitigate it with a new one-entry RSB stuffing mechanism and a new LFENCE. == Background == Indirect Branch Restricted Speculation (IBRS) was designed to help mitigate Branch Target Injection and Speculative Store Bypass, i.e. Spectre, attacks. IBRS prevents software run in less privileged modes from affecting branch prediction in more privileged modes. IBRS requires the MSR to be written on every privilege level change. To overcome some of the performance issues of IBRS, Enhanced IBRS was introduced. eIBRS is an "always on" IBRS, in other words, just turn it on once instead of writing the MSR on every privilege level change. When eIBRS is enabled, more privileged modes should be protected from less privileged modes, including protecting VMMs from guests. == Problem == Here's a simplification of how guests are run on Linux' KVM: void run_kvm_guest(void) { // Prepare to run guest VMRESUME(); // Clean up after guest runs } The execution flow for that would look something like this to the processor: 1. Host-side: call run_kvm_guest() 2. Host-side: VMRESUME 3. Guest runs, does "CALL guest_function" 4. VM exit, host runs again 5. Host might make some "cleanup" function calls 6. Host-side: RET from run_kvm_guest() Now, when back on the host, there are a couple of possible scenarios of post-guest activity the host needs to do before executing host code: * on pre-eIBRS hardware (legacy IBRS, or nothing at all), the RSB is not touched and Linux has to do a 32-entry stuffing. * on eIBRS hardware, VM exit with IBRS enabled, or restoring the host IBRS=1 shortly after VM exit, has a documented side effect of flushing the RSB except in this PBRSB situation where the software needs to stuff the last RSB entry "by hand". IOW, with eIBRS supported, host RET instructions should no longer be influenced by guest behavior after the host retires a single CALL instruction. However, if the RET instructions are "unbalanced" with CALLs after a VM exit as is the RET in #6, it might speculatively use the address for the instruction after the CALL in #3 as an RSB prediction. This is a problem since the (untrusted) guest controls this address. Balanced CALL/RET instruction pairs such as in step #5 are not affected. == Solution == The PBRSB issue affects a wide variety of Intel processors which support eIBRS. But not all of them need mitigation. Today, X86_FEATURE_RSB_VMEXIT triggers an RSB filling sequence that mitigates PBRSB. Systems setting RSB_VMEXIT need no further mitigation - i.e., eIBRS systems which enable legacy IBRS explicitly. However, such systems (X86_FEATURE_IBRS_ENHANCED) do not set RSB_VMEXIT and most of them need a new mitigation. Therefore, introduce a new feature flag X86_FEATURE_RSB_VMEXIT_LITE which triggers a lighter-weight PBRSB mitigation versus RSB_VMEXIT. The lighter-weight mitigation performs a CALL instruction which is immediately followed by a speculative execution barrier (INT3). This steers speculative execution to the barrier -- just like a retpoline -- which ensures that speculation can never reach an unbalanced RET. Then, ensure this CALL is retired before continuing execution with an LFENCE. In other words, the window of exposure is opened at VM exit where RET behavior is troublesome. While the window is open, force RSB predictions sampling for RET targets to a dead end at the INT3. Close the window with the LFENCE. There is a subset of eIBRS systems which are not vulnerable to PBRSB. Add these systems to the cpu_vuln_whitelist[] as NO_EIBRS_PBRSB. Future systems that aren't vulnerable will set ARCH_CAP_PBRSB_NO. [ bp: Massage, incorporate review comments from Andy Cooper. ] Signed-off-by: Daniel Sneddon Co-developed-by: Pawan Gupta Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov Signed-off-by: Greg Kroah-Hartman

tools headers cpufeatures: Sync with the kernel sources

2022-07-23T10:54:13+00:00

commit f098addbdb44c8a565367f5162f3ab170ed9404a upstream. To pick the changes from: f43b9876e857c739 ("x86/retbleed: Add fine grained Kconfig knobs") a149180fbcf336e9 ("x86: Add magic AMD return-thunk") 15e67227c49a5783 ("x86: Undo return-thunk damage") 369ae6ffc41a3c11 ("x86/retpoline: Cleanup some #ifdefery") 4ad3278df6fe2b08 x86/speculation: Disable RRSBA behavior 26aae8ccbc197223 x86/cpu/amd: Enumerate BTC_NO 9756bba28470722d x86/speculation: Fill RSB on vmexit for IBRS 3ebc170068885b6f x86/bugs: Add retbleed=ibpb 2dbb887e875b1de3 x86/entry: Add kernel IBRS implementation 6b80b59b35557065 x86/bugs: Report AMD retbleed vulnerability a149180fbcf336e9 x86: Add magic AMD return-thunk 15e67227c49a5783 x86: Undo return-thunk damage a883d624aed463c8 x86/cpufeatures: Move RETPOLINE flags to word 11 51802186158c74a0 x86/speculation/mmio: Enumerate Processor MMIO Stale Data bug This only causes these perf files to be rebuilt: CC /tmp/build/perf/bench/mem-memcpy-x86-64-asm.o CC /tmp/build/perf/bench/mem-memset-x86-64-asm.o And addresses this perf build warning: Warning: Kernel ABI header at 'tools/arch/x86/include/asm/cpufeatures.h' differs from latest version at 'arch/x86/include/asm/cpufeatures.h' diff -u tools/arch/x86/include/asm/cpufeatures.h arch/x86/include/asm/cpufeatures.h Warning: Kernel ABI header at 'tools/arch/x86/include/asm/disabled-features.h' differs from latest version at 'arch/x86/include/asm/disabled-features.h' diff -u tools/arch/x86/include/asm/disabled-features.h arch/x86/include/asm/disabled-features.h Cc: Adrian Hunter Cc: Borislav Petkov Cc: Ian Rogers Cc: Jiri Olsa Cc: Namhyung Kim Cc: Peter Zijlstra Signed-off-by: Greg Kroah-Hartman

tools arch x86: Sync the msr-index.h copy with the kernel sources

2022-07-23T10:54:13+00:00

commit 91d248c3b903b46a58cbc7e8d38d684d3e4007c2 upstream. To pick up the changes from these csets: 4ad3278df6fe2b08 ("x86/speculation: Disable RRSBA behavior") d7caac991feeef1b ("x86/cpu/amd: Add Spectral Chicken") That cause no changes to tooling: $ tools/perf/trace/beauty/tracepoints/x86_msr.sh > before $ cp arch/x86/include/asm/msr-index.h tools/arch/x86/include/asm/msr-index.h $ tools/perf/trace/beauty/tracepoints/x86_msr.sh > after $ diff -u before after $ Just silences this perf build warning: Warning: Kernel ABI header at 'tools/arch/x86/include/asm/msr-index.h' differs from latest version at 'arch/x86/include/asm/msr-index.h' diff -u tools/arch/x86/include/asm/msr-index.h arch/x86/include/asm/msr-index.h Cc: Adrian Hunter Cc: Borislav Petkov Cc: Ian Rogers Cc: Jiri Olsa Cc: Namhyung Kim Cc: Pawan Gupta Cc: Peter Zijlstra Link: https://lore.kernel.org/lkml/YtQTm9wsB3hxQWvy@kernel.org Signed-off-by: Arnaldo Carvalho de Melo Signed-off-by: Greg Kroah-Hartman

x86/speculation: Disable RRSBA behavior

2022-07-23T10:54:11+00:00

commit 4ad3278df6fe2b0852b00d5757fc2ccd8e92c26e upstream. Some Intel processors may use alternate predictors for RETs on RSB-underflow. This condition may be vulnerable to Branch History Injection (BHI) and intramode-BTI. Kernel earlier added spectre_v2 mitigation modes (eIBRS+Retpolines, eIBRS+LFENCE, Retpolines) which protect indirect CALLs and JMPs against such attacks. However, on RSB-underflow, RET target prediction may fallback to alternate predictors. As a result, RET's predicted target may get influenced by branch history. A new MSR_IA32_SPEC_CTRL bit (RRSBA_DIS_S) controls this fallback behavior when in kernel mode. When set, RETs will not take predictions from alternate predictors, hence mitigating RETs as well. Support for this is enumerated by CPUID.7.2.EDX[RRSBA_CTRL] (bit2). For spectre v2 mitigation, when a user selects a mitigation that protects indirect CALLs and JMPs against BHI and intramode-BTI, set RRSBA_DIS_S also to protect RETs for RSB-underflow case. Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov [cascardo: no X86_FEATURE_INTEL_PPIN] Signed-off-by: Thadeu Lima de Souza Cascardo Signed-off-by: Greg Kroah-Hartman

KVM: x86/speculation: Disable Fill buffer clear within guests

2022-06-16T11:30:34+00:00

commit 027bbb884be006b05d9c577d6401686053aa789e upstream The enumeration of MD_CLEAR in CPUID(EAX=7,ECX=0).EDX{bit 10} is not an accurate indicator on all CPUs of whether the VERW instruction will overwrite fill buffers. FB_CLEAR enumeration in IA32_ARCH_CAPABILITIES{bit 17} covers the case of CPUs that are not vulnerable to MDS/TAA, indicating that microcode does overwrite fill buffers. Guests running in VMM environments may not be aware of all the capabilities/vulnerabilities of the host CPU. Specifically, a guest may apply MDS/TAA mitigations when a virtual CPU is enumerated as vulnerable to MDS/TAA even when the physical CPU is not. On CPUs that enumerate FB_CLEAR_CTRL the VMM may set FB_CLEAR_DIS to skip overwriting of fill buffers by the VERW instruction. This is done by setting FB_CLEAR_DIS during VMENTER and resetting on VMEXIT. For guests that enumerate FB_CLEAR (explicitly asking for fill buffer clear capability) the VMM will not use FB_CLEAR_DIS. Irrespective of guest state, host overwrites CPU buffers before VMENTER to protect itself from an MMIO capable guest, as part of mitigation for MMIO Stale Data vulnerabilities. Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

x86/speculation/mmio: Enumerate Processor MMIO Stale Data bug

2022-06-16T11:30:32+00:00

commit 51802186158c74a0304f51ab963e7c2b3a2b046f upstream Processor MMIO Stale Data is a class of vulnerabilities that may expose data after an MMIO operation. For more details please refer to Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst Add the Processor MMIO Stale Data bug enumeration. A microcode update adds new bits to the MSR IA32_ARCH_CAPABILITIES, define them. Signed-off-by: Pawan Gupta Signed-off-by: Borislav Petkov Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman