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    Subject[PATCH v11 28/29] x86/arch_prctl: ARCH_GET_FEATURES_WITH_KERNEL_ASSISTANCE
    Date
    arch_prctl(ARCH_GET_FEATURES_WITH_KERNEL_ASSISTANCE, u64 *bitmask)
    Return the bitmask of the kernel-supported features. If XSAVE is
    disabled, the bitmask indicates only legacy states.

    Suggested-by: Borislav Petkov <bp@suse.de>
    Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
    Cc: x86@kernel.org
    Cc: linux-kernel@vger.kernel.org
    ---
    Changes from v9:
    * Add as a new patch. (Thiago Macieira and Borislav Petkov)
    ---
    arch/x86/include/uapi/asm/prctl.h | 23 +++++++++++----------
    arch/x86/kernel/fpu/xstate.c | 34 ++++++++++++++++++++-----------
    arch/x86/kernel/process.c | 1 +
    3 files changed, 35 insertions(+), 23 deletions(-)

    diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
    index c73e141ce90a..6912d5fe85f3 100644
    --- a/arch/x86/include/uapi/asm/prctl.h
    +++ b/arch/x86/include/uapi/asm/prctl.h
    @@ -2,19 +2,20 @@
    #ifndef _ASM_X86_PRCTL_H
    #define _ASM_X86_PRCTL_H

    -#define ARCH_SET_GS 0x1001
    -#define ARCH_SET_FS 0x1002
    -#define ARCH_GET_FS 0x1003
    -#define ARCH_GET_GS 0x1004
    +#define ARCH_SET_GS 0x1001
    +#define ARCH_SET_FS 0x1002
    +#define ARCH_GET_FS 0x1003
    +#define ARCH_GET_GS 0x1004

    -#define ARCH_GET_CPUID 0x1011
    -#define ARCH_SET_CPUID 0x1012
    +#define ARCH_GET_CPUID 0x1011
    +#define ARCH_SET_CPUID 0x1012

    -#define ARCH_SET_STATE_ENABLE 0x1021
    -#define ARCH_GET_STATE_ENABLE 0x1022
    +#define ARCH_GET_FEATURES_WITH_KERNEL_ASSISTANCE 0x1020
    +#define ARCH_SET_STATE_ENABLE 0x1021
    +#define ARCH_GET_STATE_ENABLE 0x1022

    -#define ARCH_MAP_VDSO_X32 0x2001
    -#define ARCH_MAP_VDSO_32 0x2002
    -#define ARCH_MAP_VDSO_64 0x2003
    +#define ARCH_MAP_VDSO_X32 0x2001
    +#define ARCH_MAP_VDSO_32 0x2002
    +#define ARCH_MAP_VDSO_64 0x2003

    #endif /* _ASM_X86_PRCTL_H */
    diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
    index 81566a18643b..75db4def5ec5 100644
    --- a/arch/x86/kernel/fpu/xstate.c
    +++ b/arch/x86/kernel/fpu/xstate.c
    @@ -1299,6 +1299,24 @@ int realloc_xstate_buffer(struct fpu *fpu, u64 mask)
    return 0;
    }

    +/**
    + * get_features_mask_uabi - Get a feature list that the kernel supports
    + * Return: A bitmap that indicates which state the kernel enabled.
    + */
    +static u64 get_features_mask_uabi(void)
    +{
    + if (!cpu_feature_enabled(X86_FEATURE_FPU))
    + return 0;
    +
    + if (use_xsave())
    + return xfeatures_mask_uabi();
    +
    + if (use_fxsr())
    + return XFEATURE_MASK_FPSSE;
    +
    + return XFEATURE_MASK_FP;
    +}
    +
    /**
    * reset_state_perm - Reset a task's permission for dynamic user state
    *
    @@ -1329,7 +1347,7 @@ void reset_state_perm(struct task_struct *tsk)
    }

    /**
    - * do_arch_prctl_state - Read or write the state permission.
    + * do_arch_prctl_state - Handle xstate-related buffer or usage control
    * @fpu: A struct task_struct * pointer
    * @option: A subfunction of arch_prctl()
    * @arg2: Either a pointer to userspace memory or state-component
    @@ -1338,22 +1356,14 @@ void reset_state_perm(struct task_struct *tsk)
    */
    long do_arch_prctl_state(struct task_struct *tsk, int option, unsigned long arg2)
    {
    - u64 features_mask;
    -
    - if (!cpu_feature_enabled(X86_FEATURE_FPU))
    - features_mask = 0;
    - else if (use_fxsr())
    - features_mask = XFEATURE_MASK_FPSSE;
    - else
    - features_mask = XFEATURE_MASK_FP;
    + u64 features_mask = get_features_mask_uabi();

    switch (option) {
    + case ARCH_GET_FEATURES_WITH_KERNEL_ASSISTANCE:
    + return put_user(features_mask, (unsigned long __user *)arg2);
    case ARCH_SET_STATE_ENABLE: {
    u64 state_perm = arg2;

    - if (use_xsave())
    - features_mask = xfeatures_mask_uabi();
    -
    if (state_perm & ~features_mask)
    return -EINVAL;

    diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
    index b43e2b0f52f2..ae53ffd76882 100644
    --- a/arch/x86/kernel/process.c
    +++ b/arch/x86/kernel/process.c
    @@ -1023,6 +1023,7 @@ long do_arch_prctl_common(struct task_struct *task, int option,
    return get_cpuid_mode();
    case ARCH_SET_CPUID:
    return set_cpuid_mode(task, arg2);
    + case ARCH_GET_FEATURES_WITH_KERNEL_ASSISTANCE:
    case ARCH_SET_STATE_ENABLE:
    case ARCH_GET_STATE_ENABLE:
    return do_arch_prctl_state(task, option, arg2);
    --
    2.17.1
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