The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 2848ff28d180bd63a95da8e5dcbcdd76c1beeb7b # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024090809-plaything-sash-1d57@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

2848ff28d180 ("x86/fpu: Avoid writing LBR bit to IA32_XSS unless supported") c33f0a81a2cf ("x86/fpu: Add fpu_state_config::legacy_features") d72c87018d00 ("x86/fpu/xstate: Move remaining xfeature helpers to core") eda32f4f93b4 ("x86/fpu: Rework restore_regs_from_fpstate()") daddee247319 ("x86/fpu: Mop up xfeatures_mask_uabi()") 1c253ff2287f ("x86/fpu: Move xstate feature masks to fpu_*_cfg") 2bd264bce238 ("x86/fpu: Move xstate size to fpu_*_cfg") cd9ae7617449 ("x86/fpu/xstate: Cleanup size calculations") 617473acdfe4 ("x86/fpu: Cleanup fpu__init_system_xstate_size_legacy()") 578971f4e228 ("x86/fpu: Provide struct fpu_config") 5509cc78080d ("x86/fpu/signal: Use fpstate for size and features") ad6ede407aae ("x86/fpu: Use fpstate in fpu_copy_kvm_uabi_to_fpstate()") be31dfdfd75b ("x86/fpu: Use fpstate::size") 248452ce21ae ("x86/fpu: Add size and mask information to fpstate") 2dd8eedc80b1 ("x86/process: Move arch_thread_struct_whitelist() out of line") c20942ce5128 ("x86/fpu/core: Convert to fpstate") 7e049e8b7459 ("x86/fpu/signal: Convert to fpstate") 087df48c298c ("x86/fpu: Replace KVMs xstate component clearing") 18b3fa1ad15f ("x86/fpu: Convert restore_fpregs_from_fpstate() to struct fpstate") f83ac56acdad ("x86/fpu: Convert fpstate_init() to struct fpstate")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2848ff28d180bd63a95da8e5dcbcdd76c1beeb7b Mon Sep 17 00:00:00 2001 From: Mitchell Levy levymitchell0@gmail.com Date: Mon, 12 Aug 2024 13:44:12 -0700 Subject: [PATCH] x86/fpu: Avoid writing LBR bit to IA32_XSS unless supported

There are two distinct CPU features related to the use of XSAVES and LBR: whether LBR is itself supported and whether XSAVES supports LBR. The LBR subsystem correctly checks both in intel_pmu_arch_lbr_init(), but the XSTATE subsystem does not.

The LBR bit is only removed from xfeatures_mask_independent when LBR is not supported by the CPU, but there is no validation of XSTATE support.

If XSAVES does not support LBR the write to IA32_XSS causes a #GP fault, leaving the state of IA32_XSS unchanged, i.e. zero. The fault is handled with a warning and the boot continues.

Consequently the next XRSTORS which tries to restore supervisor state fails with #GP because the RFBM has zero for all supervisor features, which does not match the XCOMP_BV field.

As XFEATURE_MASK_FPSTATE includes supervisor features setting up the FPU causes a #GP, which ends up in fpu_reset_from_exception_fixup(). That fails due to the same problem resulting in recursive #GPs until the kernel runs out of stack space and double faults.

Prevent this by storing the supported independent features in fpu_kernel_cfg during XSTATE initialization and use that cached value for retrieving the independent feature bits to be written into IA32_XSS.

[ tglx: Massaged change log ]

Fixes: f0dccc9da4c0 ("x86/fpu/xstate: Support dynamic supervisor feature for LBR") Suggested-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Mitchell Levy levymitchell0@gmail.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20240812-xsave-lbr-fix-v3-1-95bac1bf62f4@gmail.c...

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index eb17f31b06d2..de16862bf230 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -591,6 +591,13 @@ struct fpu_state_config { * even without XSAVE support, i.e. legacy features FP + SSE */ u64 legacy_features; + /* + * @independent_features: + * + * Features that are supported by XSAVES, but not managed as part of + * the FPU core, such as LBR + */ + u64 independent_features; };

/* FPU state configuration information */ diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index c5a026fee5e0..1339f8328db5 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -788,6 +788,9 @@ void __init fpu__init_system_xstate(unsigned int legacy_size) goto out_disable; }

+ fpu_kernel_cfg.independent_features = fpu_kernel_cfg.max_features & + XFEATURE_MASK_INDEPENDENT; + /* * Clear XSAVE features that are disabled in the normal CPUID. */ diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h index 2ee0b9c53dcc..afb404cd2059 100644 --- a/arch/x86/kernel/fpu/xstate.h +++ b/arch/x86/kernel/fpu/xstate.h @@ -62,9 +62,9 @@ static inline u64 xfeatures_mask_supervisor(void) static inline u64 xfeatures_mask_independent(void) { if (!cpu_feature_enabled(X86_FEATURE_ARCH_LBR)) - return XFEATURE_MASK_INDEPENDENT & ~XFEATURE_MASK_LBR; + return fpu_kernel_cfg.independent_features & ~XFEATURE_MASK_LBR;

- return XFEATURE_MASK_INDEPENDENT; + return fpu_kernel_cfg.independent_features; }

/* XSAVE/XRSTOR wrapper functions */