From: Daniel Sneddon daniel.sneddon@linux.intel.com

mainline inclusion from mainline-v6.5-rc6 commit 553a5c03e90a6087e88f8ff878335ef0621536fb category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I7XLNT CVE: CVE-2022-40982

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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commit 553a5c03e90a6087e88f8ff878335ef0621536fb upstream

The Gather Data Sampling (GDS) vulnerability allows malicious software to infer stale data previously stored in vector registers. This may include sensitive data such as cryptographic keys. GDS is mitigated in microcode, and systems with up-to-date microcode are protected by default. However, any affected system that is running with older microcode will still be vulnerable to GDS attacks.

Since the gather instructions used by the attacker are part of the AVX2 and AVX512 extensions, disabling these extensions prevents gather instructions from being executed, thereby mitigating the system from GDS. Disabling AVX2 is sufficient, but we don't have the granularity to do this. The XCR0[2] disables AVX, with no option to just disable AVX2.

Add a kernel parameter gather_data_sampling=force that will enable the microcode mitigation if available, otherwise it will disable AVX on affected systems.

This option will be ignored if cmdline mitigations=off.

This is a *big* hammer. It is known to break buggy userspace that uses incomplete, buggy AVX enumeration. Unfortunately, such userspace does exist in the wild:

https://www.mail-archive.com/bug-coreutils@gnu.org/msg33046.html

[ dhansen: add some more ominous warnings about disabling AVX ]

Signed-off-by: Daniel Sneddon daniel.sneddon@linux.intel.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Acked-by: Josh Poimboeuf jpoimboe@kernel.org Signed-off-by: Daniel Sneddon daniel.sneddon@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Zeng Heng zengheng4@huawei.com --- .../hw-vuln/gather_data_sampling.rst | 18 +++++++++++++---- .../admin-guide/kernel-parameters.txt | 8 +++++++- arch/x86/kernel/cpu/bugs.c | 20 ++++++++++++++++++- 3 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/Documentation/admin-guide/hw-vuln/gather_data_sampling.rst b/Documentation/admin-guide/hw-vuln/gather_data_sampling.rst index 74dab6af7fe1..40b7a6260010 100644 --- a/Documentation/admin-guide/hw-vuln/gather_data_sampling.rst +++ b/Documentation/admin-guide/hw-vuln/gather_data_sampling.rst @@ -60,14 +60,21 @@ bits: ================================ === ============================

GDS can also be mitigated on systems that don't have updated microcode by -disabling AVX. This can be done by setting "clearcpuid=avx" on the kernel -command-line. +disabling AVX. This can be done by setting gather_data_sampling="force" or +"clearcpuid=avx" on the kernel command-line. + +If used, these options will disable AVX use by turning on 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.

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. +"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.

GDS System Information ------------------------ @@ -83,6 +90,9 @@ The possible values contained in this file are: 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 diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index d757d806c2e0..0f6d53539111 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1483,7 +1483,13 @@

This issue is mitigated by default in updated microcode. The mitigation may have a performance impact but can be - disabled. + disabled. On systems without the microcode mitigation + disabling AVX serves as a mitigation. + + force: Disable AVX to mitigate systems without + microcode mitigation. No effect if the microcode + mitigation is present. Known to cause crashes in + userspace with buggy AVX enumeration.

off: Disable GDS mitigation.

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index fecb1c127327..1c90239ff088 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -649,6 +649,7 @@ early_param("srbds", srbds_parse_cmdline); enum gds_mitigations { GDS_MITIGATION_OFF, GDS_MITIGATION_UCODE_NEEDED, + GDS_MITIGATION_FORCE, GDS_MITIGATION_FULL, GDS_MITIGATION_FULL_LOCKED, GDS_MITIGATION_HYPERVISOR, @@ -659,6 +660,7 @@ static enum gds_mitigations gds_mitigation __ro_after_init = GDS_MITIGATION_FULL static const char * const gds_strings[] = { [GDS_MITIGATION_OFF] = "Vulnerable", [GDS_MITIGATION_UCODE_NEEDED] = "Vulnerable: No microcode", + [GDS_MITIGATION_FORCE] = "Mitigation: AVX disabled, no microcode", [GDS_MITIGATION_FULL] = "Mitigation: Microcode", [GDS_MITIGATION_FULL_LOCKED] = "Mitigation: Microcode (locked)", [GDS_MITIGATION_HYPERVISOR] = "Unknown: Dependent on hypervisor status", @@ -684,6 +686,7 @@ void update_gds_msr(void) rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl); mcu_ctrl &= ~GDS_MITG_DIS; break; + case GDS_MITIGATION_FORCE: case GDS_MITIGATION_UCODE_NEEDED: case GDS_MITIGATION_HYPERVISOR: return; @@ -718,10 +721,23 @@ static void __init gds_select_mitigation(void)

/* No microcode */ if (!(x86_read_arch_cap_msr() & ARCH_CAP_GDS_CTRL)) { - gds_mitigation = GDS_MITIGATION_UCODE_NEEDED; + if (gds_mitigation == GDS_MITIGATION_FORCE) { + /* + * This only needs to be done on the boot CPU so do it + * here rather than in update_gds_msr() + */ + setup_clear_cpu_cap(X86_FEATURE_AVX); + pr_warn("Microcode update needed! Disabling AVX as mitigation.\n"); + } else { + gds_mitigation = GDS_MITIGATION_UCODE_NEEDED; + } goto out; }

+ /* Microcode has mitigation, use it */ + if (gds_mitigation == GDS_MITIGATION_FORCE) + gds_mitigation = GDS_MITIGATION_FULL; + rdmsrl(MSR_IA32_MCU_OPT_CTRL, mcu_ctrl); if (mcu_ctrl & GDS_MITG_LOCKED) { if (gds_mitigation == GDS_MITIGATION_OFF) @@ -752,6 +768,8 @@ static int __init gds_parse_cmdline(char *str)

if (!strcmp(str, "off")) gds_mitigation = GDS_MITIGATION_OFF; + else if (!strcmp(str, "force")) + gds_mitigation = GDS_MITIGATION_FORCE;

return 0; }

From: Daniel Sneddon daniel.sneddon@linux.intel.com

mainline inclusion from mainline-v6.5-rc6 commit 81ac7e5d741742d650b4ed6186c4826c1a0631a7 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I7XLNT CVE: CVE-2022-40982

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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commit 81ac7e5d741742d650b4ed6186c4826c1a0631a7 upstream

Gather Data Sampling (GDS) is a transient execution attack using gather instructions from the AVX2 and AVX512 extensions. This attack allows malicious code to infer data that was previously stored in vector registers. Systems that are not vulnerable to GDS will set the GDS_NO bit of the IA32_ARCH_CAPABILITIES MSR. This is useful for VM guests that may think they are on vulnerable systems that are, in fact, not affected. Guests that are running on affected hosts where the mitigation is enabled are protected as if they were running on an unaffected system.

On all hosts that are not affected or that are mitigated, set the GDS_NO bit.

Signed-off-by: Daniel Sneddon daniel.sneddon@linux.intel.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Acked-by: Josh Poimboeuf jpoimboe@kernel.org Signed-off-by: Daniel Sneddon daniel.sneddon@linux.intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Conflicts: arch/x86/kvm/x86.c Signed-off-by: Zeng Heng zengheng4@huawei.com --- arch/x86/kernel/cpu/bugs.c | 7 +++++++ arch/x86/kvm/x86.c | 5 +++++ 2 files changed, 12 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index f5b1020187cc..1cc7c7419aa4 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -670,6 +670,13 @@ static const char * const gds_strings[] = { [GDS_MITIGATION_HYPERVISOR] = "Unknown: Dependent on hypervisor status", };

+bool gds_ucode_mitigated(void) +{ + return (gds_mitigation == GDS_MITIGATION_FULL || + gds_mitigation == GDS_MITIGATION_FULL_LOCKED); +} +EXPORT_SYMBOL_GPL(gds_ucode_mitigated); + void update_gds_msr(void) { u64 mcu_ctrl_after; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 1a5230d44dd9..8b5844539fa0 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -305,6 +305,8 @@ static struct kmem_cache *x86_fpu_cache;

static struct kmem_cache *x86_emulator_cache;

+extern bool gds_ucode_mitigated(void); + /* * When called, it means the previous get/set msr reached an invalid msr. * Return true if we want to ignore/silent this failed msr access. @@ -1472,6 +1474,9 @@ static u64 kvm_get_arch_capabilities(void) /* Guests don't need to know "Fill buffer clear control" exists */ data &= ~ARCH_CAP_FB_CLEAR_CTRL;

+ if (!boot_cpu_has_bug(X86_BUG_GDS) || gds_ucode_mitigated()) + data |= ARCH_CAP_GDS_NO; + return data; }

From: Arnd Bergmann arnd@arndb.de

mainline inclusion from mainline-v6.5-rc6 commit eb3515dc99c7c85f4170b50838136b2a193f8012 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I7XLNT CVE: CVE-2022-40982

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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The declaration got placed in the .c file of the caller, but that causes a warning for the definition:

arch/x86/kernel/cpu/bugs.c:682:6: error: no previous prototype for 'gds_ucode_mitigated' [-Werror=missing-prototypes]

Move it to a header where both sides can observe it instead.

Fixes: 81ac7e5d74174 ("KVM: Add GDS_NO support to KVM") Signed-off-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Tested-by: Daniel Sneddon daniel.sneddon@linux.intel.com Cc: stable@kernel.org Link: https://lore.kernel.org/all/20230809130530.1913368-2-arnd%40kernel.org Signed-off-by: Zeng Heng zengheng4@huawei.com --- arch/x86/include/asm/processor.h | 2 ++ arch/x86/kvm/x86.c | 2 -- 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h index d428d611a43a..f00203c489e6 100644 --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -858,4 +858,6 @@ enum mds_mitigations { MDS_MITIGATION_VMWERV, };

+extern bool gds_ucode_mitigated(void); + #endif /* _ASM_X86_PROCESSOR_H */ diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 8b5844539fa0..30cda214fbff 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -305,8 +305,6 @@ static struct kmem_cache *x86_fpu_cache;

static struct kmem_cache *x86_emulator_cache;

-extern bool gds_ucode_mitigated(void); - /* * When called, it means the previous get/set msr reached an invalid msr. * Return true if we want to ignore/silent this failed msr access.