x86, fpu: use non-lazy fpu restore for processors supporting xsave

[mirror_ubuntu-artful-kernel.git] / arch / x86 / kernel / xsave.c

/*
 * xsave/xrstor support.
 *
 * Author: Suresh Siddha <suresh.b.siddha@intel.com>
 */

#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_checking((__force void *) 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_checking((__force void *) buf);
        } else
                return frstor_checking((__force void *) 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_xsave())
                        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)
{
        clts();
        set_in_cr4(X86_CR4_OSXSAVE);
        xsetbv(XCR_XFEATURE_ENABLED_MASK, pcntxt_mask);
}

/*
 * This is same as math_state_restore(). But use_xsave() is not yet
 * patched to use math_state_restore().
 */
static inline void init_restore_xstate(void)
{
        init_fpu(current);
        __thread_fpu_begin(current);
        xrstor_state(init_xstate_buf, -1);
}

static inline void xstate_enable_ap(void)
{
        xstate_enable();
        init_restore_xstate();
}

/*
 * 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_xstate_init(void)
{
        setup_xstate_features();

        /*
         * 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));
        init_xstate_buf->i387.mxcsr = MXCSR_DEFAULT;

        /*
         * 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);
}

/*
 * 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_xstate_init();

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

        current->thread.fpu.state =
             alloc_bootmem_align(xstate_size, __alignof__(struct xsave_struct));
        init_restore_xstate();
}

/*
 * 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_ap;
        this_func();
}