diff options
| -rw-r--r-- | Documentation/x86/xstate.rst | 9 | ||||
| -rw-r--r-- | arch/x86/include/asm/fpu/xcr.h | 12 | ||||
| -rw-r--r-- | arch/x86/include/asm/fpu/xstate.h | 7 | ||||
| -rw-r--r-- | arch/x86/kernel/cpu/cpuid-deps.c | 1 | ||||
| -rw-r--r-- | arch/x86/kernel/fpu/xstate.h | 37 |
5 files changed, 64 insertions, 2 deletions
diff --git a/Documentation/x86/xstate.rst b/Documentation/x86/xstate.rst index 65de3f054ba5..5cec7fb558d6 100644 --- a/Documentation/x86/xstate.rst +++ b/Documentation/x86/xstate.rst @@ -63,3 +63,12 @@ kernel sends SIGILL to the application. If the process has permission then the handler allocates a larger xstate buffer for the task so the large state can be context switched. In the unlikely cases that the allocation fails, the kernel sends SIGSEGV. + +Dynamic features in signal frames +--------------------------------- + +Dynamcally enabled features are not written to the signal frame upon signal +entry if the feature is in its initial configuration. This differs from +non-dynamic features which are always written regardless of their +configuration. Signal handlers can examine the XSAVE buffer's XSTATE_BV +field to determine if a features was written. diff --git a/arch/x86/include/asm/fpu/xcr.h b/arch/x86/include/asm/fpu/xcr.h index 79f95d3787e2..9656a5bc6fea 100644 --- a/arch/x86/include/asm/fpu/xcr.h +++ b/arch/x86/include/asm/fpu/xcr.h @@ -3,6 +3,7 @@ #define _ASM_X86_FPU_XCR_H #define XCR_XFEATURE_ENABLED_MASK 0x00000000 +#define XCR_XFEATURE_IN_USE_MASK 0x00000001 static inline u64 xgetbv(u32 index) { @@ -20,4 +21,15 @@ static inline void xsetbv(u32 index, u64 value) asm volatile("xsetbv" :: "a" (eax), "d" (edx), "c" (index)); } +/* + * Return a mask of xfeatures which are currently being tracked + * by the processor as being in the initial configuration. + * + * Callers should check X86_FEATURE_XGETBV1. + */ +static inline u64 xfeatures_in_use(void) +{ + return xgetbv(XCR_XFEATURE_IN_USE_MASK); +} + #endif /* _ASM_X86_FPU_XCR_H */ diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h index 0f8b90ab18c9..cd3dd170e23a 100644 --- a/arch/x86/include/asm/fpu/xstate.h +++ b/arch/x86/include/asm/fpu/xstate.h @@ -92,6 +92,13 @@ #define XFEATURE_MASK_FPSTATE (XFEATURE_MASK_USER_RESTORE | \ XFEATURE_MASK_SUPERVISOR_SUPPORTED) +/* + * Features in this mask have space allocated in the signal frame, but may not + * have that space initialized when the feature is in its init state. + */ +#define XFEATURE_MASK_SIGFRAME_INITOPT (XFEATURE_MASK_XTILE | \ + XFEATURE_MASK_USER_DYNAMIC) + extern u64 xstate_fx_sw_bytes[USER_XSTATE_FX_SW_WORDS]; extern void __init update_regset_xstate_info(unsigned int size, diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c index cb2fdd130aae..c881bcafba7d 100644 --- a/arch/x86/kernel/cpu/cpuid-deps.c +++ b/arch/x86/kernel/cpu/cpuid-deps.c @@ -76,6 +76,7 @@ static const struct cpuid_dep cpuid_deps[] = { { X86_FEATURE_SGX1, X86_FEATURE_SGX }, { X86_FEATURE_SGX2, X86_FEATURE_SGX1 }, { X86_FEATURE_XFD, X86_FEATURE_XSAVES }, + { X86_FEATURE_XFD, X86_FEATURE_XGETBV1 }, { X86_FEATURE_AMX_TILE, X86_FEATURE_XFD }, {} }; diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h index e18210dff88c..86ea7c0fa2f6 100644 --- a/arch/x86/kernel/fpu/xstate.h +++ b/arch/x86/kernel/fpu/xstate.h @@ -4,6 +4,7 @@ #include <asm/cpufeature.h> #include <asm/fpu/xstate.h> +#include <asm/fpu/xcr.h> #ifdef CONFIG_X86_64 DECLARE_PER_CPU(u64, xfd_state); @@ -199,6 +200,32 @@ static inline void os_xrstor_supervisor(struct fpstate *fpstate) } /* + * XSAVE itself always writes all requested xfeatures. Removing features + * from the request bitmap reduces the features which are written. + * Generate a mask of features which must be written to a sigframe. The + * unset features can be optimized away and not written. + * + * This optimization is user-visible. Only use for states where + * uninitialized sigframe contents are tolerable, like dynamic features. + * + * Users of buffers produced with this optimization must check XSTATE_BV + * to determine which features have been optimized out. + */ +static inline u64 xfeatures_need_sigframe_write(void) +{ + u64 xfeaures_to_write; + + /* In-use features must be written: */ + xfeaures_to_write = xfeatures_in_use(); + + /* Also write all non-optimizable sigframe features: */ + xfeaures_to_write |= XFEATURE_MASK_USER_SUPPORTED & + ~XFEATURE_MASK_SIGFRAME_INITOPT; + + return xfeaures_to_write; +} + +/* * Save xstate to user space xsave area. * * We don't use modified optimization because xrstor/xrstors might track @@ -220,10 +247,16 @@ static inline int xsave_to_user_sigframe(struct xregs_state __user *buf) */ struct fpstate *fpstate = current->thread.fpu.fpstate; u64 mask = fpstate->user_xfeatures; - u32 lmask = mask; - u32 hmask = mask >> 32; + u32 lmask; + u32 hmask; int err; + /* Optimize away writing unnecessary xfeatures: */ + if (fpu_state_size_dynamic()) + mask &= xfeatures_need_sigframe_write(); + + lmask = mask; + hmask = mask >> 32; xfd_validate_state(fpstate, mask, false); stac(); |