xsave.c

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/*
 * xsave/xrstor support.
 *
 * Author: Suresh Siddha <[email protected]>
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/bootmem.h>
#include <linux/compat.h>
#include <asm/i387.h>
#include <asm/fpu-internal.h>
#include <asm/sigframe.h>
#include <asm/xcr.h>

/*
 * Supported feature mask by the CPU and the kernel.
 */
u64 pcntxt_mask;

/*
 * Represents init state for the supported extended state.
 */
struct xsave_struct *init_xstate_buf;

static struct _fpx_sw_bytes fx_sw_reserved, fx_sw_reserved_ia32;
static unsigned int *xstate_offsets, *xstate_sizes, xstate_features;

/*
 * If a processor implementation discern that a processor state component is
 * in its initialized state it may modify the corresponding bit in the
 * xsave_hdr.xstate_bv as '0', with out modifying the corresponding memory
 * layout in the case of xsaveopt. While presenting the xstate information to
 * the user, we always ensure that the memory layout of a feature will be in
 * the init state if the corresponding header bit is zero. This is to ensure
 * that the user doesn't see some stale state in the memory layout during
 * signal handling, debugging etc.
 */
void __sanitize_i387_state(struct task_struct *tsk)
{
    struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;
    int feature_bit = 0x2;
    u64 xstate_bv;

    if (!fx)
        return;

    xstate_bv = tsk->thread.fpu.state->xsave.xsave_hdr.xstate_bv;

    /*
     * None of the feature bits are in init state. So nothing else
     * to do for us, as the memory layout is up to date.
     */
    if ((xstate_bv & pcntxt_mask) == pcntxt_mask)
        return;

    /*
     * FP is in init state
     */
    if (!(xstate_bv & XSTATE_FP)) {
        fx->cwd = 0x37f;
        fx->swd = 0;
        fx->twd = 0;
        fx->fop = 0;
        fx->rip = 0;
        fx->rdp = 0;
        memset(&fx->st_space[0], 0, 128);
    }

    /*
     * SSE is in init state
     */
    if (!(xstate_bv & XSTATE_SSE))
        memset(&fx->xmm_space[0], 0, 256);

    xstate_bv = (pcntxt_mask & ~xstate_bv) >> 2;

    /*
     * Update all the other memory layouts for which the corresponding
     * header bit is in the init state.
     */
    while (xstate_bv) {
        if (xstate_bv & 0x1) {
            int offset = xstate_offsets[feature_bit];
            int size = xstate_sizes[feature_bit];

            memcpy(((void *) fx) + offset,
                   ((void *) init_xstate_buf) + offset,
                   size);
        }

        xstate_bv >>= 1;
        feature_bit++;
    }
}

/*
 * Check for the presence of extended state information in the
 * user fpstate pointer in the sigcontext.
 */
static inline int check_for_xstate(struct i387_fxsave_struct __user *buf,
                   void __user *fpstate,
                   struct _fpx_sw_bytes *fx_sw)
{
    int min_xstate_size = sizeof(struct i387_fxsave_struct) +
                  sizeof(struct xsave_hdr_struct);
    unsigned int magic2;

    if (__copy_from_user(fx_sw, &buf->sw_reserved[0], sizeof(*fx_sw)))
        return -1;

    /* Check for the first magic field and other error scenarios. */
    if (fx_sw->magic1 != FP_XSTATE_MAGIC1 ||
        fx_sw->xstate_size < min_xstate_size ||
        fx_sw->xstate_size > xstate_size ||
        fx_sw->xstate_size > fx_sw->extended_size)
        return -1;

    /*
     * Check for the presence of second magic word at the end of memory
     * layout. This detects the case where the user just copied the legacy
     * fpstate layout with out copying the extended state information
     * in the memory layout.
     */
    if (__get_user(magic2, (__u32 __user *)(fpstate + fx_sw->xstate_size))
        || magic2 != FP_XSTATE_MAGIC2)
        return -1;

    return 0;
}

/*
 * Signal frame handlers.
 */
static inline int save_fsave_header(struct task_struct *tsk, void __user *buf)
{
    if (use_fxsr()) {
        struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
        struct user_i387_ia32_struct env;
        struct _fpstate_ia32 __user *fp = buf;

        convert_from_fxsr(&env, tsk);

        if (__copy_to_user(buf, &env, sizeof(env)) ||
            __put_user(xsave->i387.swd, &fp->status) ||
            __put_user(X86_FXSR_MAGIC, &fp->magic))
            return -1;
    } else {
        struct i387_fsave_struct __user *fp = buf;
        u32 swd;
        if (__get_user(swd, &fp->swd) || __put_user(swd, &fp->status))
            return -1;
    }

    return 0;
}

static inline int save_xstate_epilog(void __user *buf, int ia32_frame)
{
    struct xsave_struct __user *x = buf;
    struct _fpx_sw_bytes *sw_bytes;
    u32 xstate_bv;
    int err;

    /* Setup the bytes not touched by the [f]xsave and reserved for SW. */
    sw_bytes = ia32_frame ? &fx_sw_reserved_ia32 : &fx_sw_reserved;
    err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));

    if (!use_xsave())
        return err;

    err |= __put_user(FP_XSTATE_MAGIC2, (__u32 *)(buf + xstate_size));

    /*
     * Read the xstate_bv which we copied (directly from the cpu or
     * from the state in task struct) to the user buffers.
     */
    err |= __get_user(xstate_bv, (__u32 *)&x->xsave_hdr.xstate_bv);

    /*
     * For legacy compatible, we always set FP/SSE bits in the bit
     * vector while saving the state to the user context. This will
     * enable us capturing any changes(during sigreturn) to
     * the FP/SSE bits by the legacy applications which don't touch
     * xstate_bv in the xsave header.
     *
     * xsave aware apps can change the xstate_bv in the xsave
     * header as well as change any contents in the memory layout.
     * xrestore as part of sigreturn will capture all the changes.
     */
    xstate_bv |= XSTATE_FPSSE;

    err |= __put_user(xstate_bv, (__u32 *)&x->xsave_hdr.xstate_bv);

    return err;
}

static inline int save_user_xstate(struct xsave_struct __user *buf)
{
    int err;

    if (use_xsave())
        err = xsave_user(buf);
    else if (use_fxsr())
        err = fxsave_user((struct i387_fxsave_struct __user *) buf);
    else
        err = fsave_user((struct i387_fsave_struct __user *) buf);

    if (unlikely(err) && __clear_user(buf, xstate_size))
        err = -EFAULT;
    return err;
}

/*
 * Save the fpu, extended register state to the user signal frame.
 *
 * 'buf_fx' is the 64-byte aligned pointer at which the [f|fx|x]save
 *  state is copied.
 *  'buf' points to the 'buf_fx' or to the fsave header followed by 'buf_fx'.
 *
 *  buf == buf_fx for 64-bit frames and 32-bit fsave frame.
 *  buf != buf_fx for 32-bit frames with fxstate.
 *
 * If the fpu, extended register state is live, save the state directly
 * to the user frame pointed by the aligned pointer 'buf_fx'. Otherwise,
 * copy the thread's fpu state to the user frame starting at 'buf_fx'.
 *
 * If this is a 32-bit frame with fxstate, put a fsave header before
 * the aligned state at 'buf_fx'.
 *
 * For [f]xsave state, update the SW reserved fields in the [f]xsave frame
 * indicating the absence/presence of the extended state to the user.
 */
int save_xstate_sig(void __user *buf, void __user *buf_fx, int size)
{
    struct xsave_struct *xsave = &current->thread.fpu.state->xsave;
    struct task_struct *tsk = current;
    int ia32_fxstate = (buf != buf_fx);

    ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
             config_enabled(CONFIG_IA32_EMULATION));

    if (!access_ok(VERIFY_WRITE, buf, size))
        return -EACCES;

    if (!HAVE_HWFP)
        return fpregs_soft_get(current, NULL, 0,
            sizeof(struct user_i387_ia32_struct), NULL,
            (struct _fpstate_ia32 __user *) buf) ? -1 : 1;

    if (user_has_fpu()) {
        /* Save the live register state to the user directly. */
        if (save_user_xstate(buf_fx))
            return -1;
        /* Update the thread's fxstate to save the fsave header. */
        if (ia32_fxstate)
            fpu_fxsave(&tsk->thread.fpu);
    } else {
        sanitize_i387_state(tsk);
        if (__copy_to_user(buf_fx, xsave, xstate_size))
            return -1;
    }

    /* Save the fsave header for the 32-bit frames. */
    if ((ia32_fxstate || !use_fxsr()) && save_fsave_header(tsk, buf))
        return -1;

    if (use_fxsr() && save_xstate_epilog(buf_fx, ia32_fxstate))
        return -1;

    drop_init_fpu(tsk); /* trigger finit */

    return 0;
}

static inline void
sanitize_restored_xstate(struct task_struct *tsk,
             struct user_i387_ia32_struct *ia32_env,
             u64 xstate_bv, int fx_only)
{
    struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
    struct xsave_hdr_struct *xsave_hdr = &xsave->xsave_hdr;

    if (use_xsave()) {
        /* These bits must be zero. */
        xsave_hdr->reserved1[0] = xsave_hdr->reserved1[1] = 0;

        /*
         * Init the state that is not present in the memory
         * layout and not enabled by the OS.
         */
        if (fx_only)
            xsave_hdr->xstate_bv = XSTATE_FPSSE;
        else
            xsave_hdr->xstate_bv &= (pcntxt_mask & xstate_bv);
    }

    if (use_fxsr()) {
        /*
         * mscsr reserved bits must be masked to zero for security
         * reasons.
         */
        xsave->i387.mxcsr &= mxcsr_feature_mask;

        convert_to_fxsr(tsk, ia32_env);
    }
}

/*
 * Restore the extended state if present. Otherwise, restore the FP/SSE state.
 */
static inline int restore_user_xstate(void __user *buf, u64 xbv, int fx_only)
{
    if (use_xsave()) {
        if ((unsigned long)buf % 64 || fx_only) {
            u64 init_bv = pcntxt_mask & ~XSTATE_FPSSE;
            xrstor_state(init_xstate_buf, init_bv);
            return fxrstor_user(buf);
        } else {
            u64 init_bv = pcntxt_mask & ~xbv;
            if (unlikely(init_bv))
                xrstor_state(init_xstate_buf, init_bv);
            return xrestore_user(buf, xbv);
        }
    } else if (use_fxsr()) {
        return fxrstor_user(buf);
    } else
        return frstor_user(buf);
}

int __restore_xstate_sig(void __user *buf, void __user *buf_fx, int size)
{
    int ia32_fxstate = (buf != buf_fx);
    struct task_struct *tsk = current;
    int state_size = xstate_size;
    u64 xstate_bv = 0;
    int fx_only = 0;

    ia32_fxstate &= (config_enabled(CONFIG_X86_32) ||
             config_enabled(CONFIG_IA32_EMULATION));

    if (!buf) {
        drop_init_fpu(tsk);
        return 0;
    }

    if (!access_ok(VERIFY_READ, buf, size))
        return -EACCES;

    if (!used_math() && init_fpu(tsk))
        return -1;

    if (!HAVE_HWFP) {
        return fpregs_soft_set(current, NULL,
                       0, sizeof(struct user_i387_ia32_struct),
                       NULL, buf) != 0;
    }

    if (use_xsave()) {
        struct _fpx_sw_bytes fx_sw_user;
        if (unlikely(check_for_xstate(buf_fx, buf_fx, &fx_sw_user))) {
            /*
             * Couldn't find the extended state information in the
             * memory layout. Restore just the FP/SSE and init all
             * the other extended state.
             */
            state_size = sizeof(struct i387_fxsave_struct);
            fx_only = 1;
        } else {
            state_size = fx_sw_user.xstate_size;
            xstate_bv = fx_sw_user.xstate_bv;
        }
    }

    if (ia32_fxstate) {
        /*
         * For 32-bit frames with fxstate, copy the user state to the
         * thread's fpu state, reconstruct fxstate from the fsave
         * header. Sanitize the copied state etc.
         */
        struct xsave_struct *xsave = &tsk->thread.fpu.state->xsave;
        struct user_i387_ia32_struct env;
        int err = 0;

        /*
         * Drop the current fpu which clears used_math(). This ensures
         * that any context-switch during the copy of the new state,
         * avoids the intermediate state from getting restored/saved.
         * Thus avoiding the new restored state from getting corrupted.
         * We will be ready to restore/save the state only after
         * set_used_math() is again set.
         */
        drop_fpu(tsk);

        if (__copy_from_user(xsave, buf_fx, state_size) ||
            __copy_from_user(&env, buf, sizeof(env))) {
            err = -1;
        } else {
            sanitize_restored_xstate(tsk, &env, xstate_bv, fx_only);
            set_used_math();
        }

        if (use_eager_fpu())
            math_state_restore();

        return err;
    } else {
        /*
         * For 64-bit frames and 32-bit fsave frames, restore the user
         * state to the registers directly (with exceptions handled).
         */
        user_fpu_begin();
        if (restore_user_xstate(buf_fx, xstate_bv, fx_only)) {
            drop_init_fpu(tsk);
            return -1;
        }
    }

    return 0;
}

/*
 * Prepare the SW reserved portion of the fxsave memory layout, indicating
 * the presence of the extended state information in the memory layout
 * pointed by the fpstate pointer in the sigcontext.
 * This will be saved when ever the FP and extended state context is
 * saved on the user stack during the signal handler delivery to the user.
 */
static void prepare_fx_sw_frame(void)
{
    int fsave_header_size = sizeof(struct i387_fsave_struct);
    int size = xstate_size + FP_XSTATE_MAGIC2_SIZE;

    if (config_enabled(CONFIG_X86_32))
        size += fsave_header_size;

    fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
    fx_sw_reserved.extended_size = size;
    fx_sw_reserved.xstate_bv = pcntxt_mask;
    fx_sw_reserved.xstate_size = xstate_size;

    if (config_enabled(CONFIG_IA32_EMULATION)) {
        fx_sw_reserved_ia32 = fx_sw_reserved;
        fx_sw_reserved_ia32.extended_size += fsave_header_size;
    }
}

/*
 * Enable the extended processor state save/restore feature
 */
static inline void xstate_enable(void)
{
    set_in_cr4(X86_CR4_OSXSAVE);
    xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
}

/*
 * Record the offsets and sizes of different state managed by the xsave
 * memory layout.
 */
static void __init setup_xstate_features(void)
{
    int eax, ebx, ecx, edx, leaf = 0x2;

    xstate_features = fls64(pcntxt_mask);
    xstate_offsets = alloc_bootmem(xstate_features * sizeof(int));
    xstate_sizes = alloc_bootmem(xstate_features * sizeof(int));

    do {
        cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx);

        if (eax == 0)
            break;

        xstate_offsets[leaf] = ebx;
        xstate_sizes[leaf] = eax;

        leaf++;
    } while (1);
}

/*
 * setup the xstate image representing the init state
 */
static void __init setup_init_fpu_buf(void)
{
    /*
     * Setup init_xstate_buf to represent the init state of
     * all the features managed by the xsave
     */
    init_xstate_buf = alloc_bootmem_align(xstate_size,
                          __alignof__(struct xsave_struct));
    fx_finit(&init_xstate_buf->i387);

    if (!cpu_has_xsave)
        return;

    setup_xstate_features();

    /*
     * Init all the features state with header_bv being 0x0
     */
    xrstor_state(init_xstate_buf, -1);
    /*
     * Dump the init state again. This is to identify the init state
     * of any feature which is not represented by all zero's.
     */
    xsave_state(init_xstate_buf, -1);
}

static enum { AUTO, ENABLE, DISABLE } eagerfpu = AUTO;
static int __init eager_fpu_setup(char *s)
{
    if (!strcmp(s, "on"))
        eagerfpu = ENABLE;
    else if (!strcmp(s, "off"))
        eagerfpu = DISABLE;
    else if (!strcmp(s, "auto"))
        eagerfpu = AUTO;
    return 1;
}
__setup("eagerfpu=", eager_fpu_setup);

/*
 * Enable and initialize the xsave feature.
 */
static void __init xstate_enable_boot_cpu(void)
{
    unsigned int eax, ebx, ecx, edx;

    if (boot_cpu_data.cpuid_level < XSTATE_CPUID) {
        WARN(1, KERN_ERR "XSTATE_CPUID missing\n");
        return;
    }

    cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
    pcntxt_mask = eax + ((u64)edx << 32);

    if ((pcntxt_mask & XSTATE_FPSSE) != XSTATE_FPSSE) {
        pr_err("FP/SSE not shown under xsave features 0x%llx\n",
               pcntxt_mask);
        BUG();
    }

    /*
     * Support only the state known to OS.
     */
    pcntxt_mask = pcntxt_mask & XCNTXT_MASK;

    xstate_enable();

    /*
     * Recompute the context size for enabled features
     */
    cpuid_count(XSTATE_CPUID, 0, &eax, &ebx, &ecx, &edx);
    xstate_size = ebx;

    update_regset_xstate_info(xstate_size, pcntxt_mask);
    prepare_fx_sw_frame();
    setup_init_fpu_buf();

    /* Auto enable eagerfpu for xsaveopt */
    if (cpu_has_xsaveopt && eagerfpu != DISABLE)
        eagerfpu = ENABLE;

    pr_info("enabled xstate_bv 0x%llx, cntxt size 0x%x\n",
        pcntxt_mask, xstate_size);
}

/*
 * For the very first instance, this calls xstate_enable_boot_cpu();
 * for all subsequent instances, this calls xstate_enable().
 *
 * This is somewhat obfuscated due to the lack of powerful enough
 * overrides for the section checks.
 */
void __cpuinit xsave_init(void)
{
    static __refdata void (*next_func)(void) = xstate_enable_boot_cpu;
    void (*this_func)(void);

    if (!cpu_has_xsave)
        return;

    this_func = next_func;
    next_func = xstate_enable;
    this_func();
}

static inline void __init eager_fpu_init_bp(void)
{
    current->thread.fpu.state =
        alloc_bootmem_align(xstate_size, __alignof__(struct xsave_struct));
    if (!init_xstate_buf)
        setup_init_fpu_buf();
}

void __cpuinit eager_fpu_init(void)
{
    static __refdata void (*boot_func)(void) = eager_fpu_init_bp;

    clear_used_math();
    current_thread_info()->status = 0;

    if (eagerfpu == ENABLE)
        setup_force_cpu_cap(X86_FEATURE_EAGER_FPU);

    if (!cpu_has_eager_fpu) {
        stts();
        return;
    }

    if (boot_func) {
        boot_func();
        boot_func = NULL;
    }

    /*
     * This is same as math_state_restore(). But use_xsave() is
     * not yet patched to use math_state_restore().
     */
    init_fpu(current);
    __thread_fpu_begin(current);
    if (cpu_has_xsave)
        xrstor_state(init_xstate_buf, -1);
    else
        fxrstor_checking(&init_xstate_buf->i387);
}