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>
#ifdef CONFIG_IA32_EMULATION
#include <asm/sigcontext32.h>
#endif
#include <asm/xcr.h>

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

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

struct _fpx_sw_bytes fx_sw_reserved;
#ifdef CONFIG_IA32_EMULATION
struct _fpx_sw_bytes fx_sw_reserved_ia32;
#endif

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)
{
	u64 xstate_bv;
	int feature_bit = 0x2;
	struct i387_fxsave_struct *fx = &tsk->thread.fpu.state->fxsave;

	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.
 */
int check_for_xstate(struct i387_fxsave_struct __user *buf,
		     void __user *fpstate,
		     struct _fpx_sw_bytes *fx_sw_user)
{
	int min_xstate_size = sizeof(struct i387_fxsave_struct) +
			      sizeof(struct xsave_hdr_struct);
	unsigned int magic2;
	int err;

	err = __copy_from_user(fx_sw_user, &buf->sw_reserved[0],
			       sizeof(struct _fpx_sw_bytes));
	if (err)
		return -EFAULT;

	/*
	 * First Magic check failed.
	 */
	if (fx_sw_user->magic1 != FP_XSTATE_MAGIC1)
		return -EINVAL;

	/*
	 * Check for error scenarios.
	 */
	if (fx_sw_user->xstate_size < min_xstate_size ||
	    fx_sw_user->xstate_size > xstate_size ||
	    fx_sw_user->xstate_size > fx_sw_user->extended_size)
		return -EINVAL;

	err = __get_user(magic2, (__u32 *) (((void *)fpstate) +
					    fx_sw_user->extended_size -
					    FP_XSTATE_MAGIC2_SIZE));
	if (err)
		return err;
	/*
	 * 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 (magic2 != FP_XSTATE_MAGIC2)
		return -EFAULT;

	return 0;
}

#ifdef CONFIG_X86_64
/*
 * Signal frame handlers.
 */

int save_i387_xstate(void __user *buf)
{
	struct task_struct *tsk = current;
	int err = 0;

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

	BUG_ON(sig_xstate_size < xstate_size);

	if ((unsigned long)buf % 64)
		pr_err("%s: bad fpstate %p\n", __func__, buf);

	if (!used_math())
		return 0;

	if (user_has_fpu()) {
		if (use_xsave())
			err = xsave_user(buf);
		else
			err = fxsave_user(buf);

		if (err)
			return err;
		user_fpu_end();
	} else {
		sanitize_i387_state(tsk);
		if (__copy_to_user(buf, &tsk->thread.fpu.state->fxsave,
				   xstate_size))
			return -1;
	}

	clear_used_math(); /* trigger finit */

	if (use_xsave()) {
		struct _fpstate __user *fx = buf;
		struct _xstate __user *x = buf;
		u64 xstate_bv;

		err = __copy_to_user(&fx->sw_reserved, &fx_sw_reserved,
				     sizeof(struct _fpx_sw_bytes));

		err |= __put_user(FP_XSTATE_MAGIC2,
				  (__u32 __user *) (buf + sig_xstate_size
						    - FP_XSTATE_MAGIC2_SIZE));

		/*
		 * Read the xstate_bv which we copied (directly from the cpu or
		 * from the state in task struct) to the user buffers and
		 * set the FP/SSE bits.
		 */
		err |= __get_user(xstate_bv, &x->xstate_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, &x->xstate_hdr.xstate_bv);

		if (err)
			return err;
	}

	return 1;
}

/*
 * Restore the extended state if present. Otherwise, restore the FP/SSE
 * state.
 */
static int restore_user_xstate(void __user *buf)
{
	struct _fpx_sw_bytes fx_sw_user;
	u64 mask;
	int err;

	if (((unsigned long)buf % 64) ||
	     check_for_xstate(buf, buf, &fx_sw_user))
		goto fx_only;

	mask = fx_sw_user.xstate_bv;

	/*
	 * restore the state passed by the user.
	 */
	err = xrestore_user(buf, mask);
	if (err)
		return err;

	/*
	 * init the state skipped by the user.
	 */
	mask = pcntxt_mask & ~mask;
	if (unlikely(mask))
		xrstor_state(init_xstate_buf, mask);

	return 0;

fx_only:
	/*
	 * couldn't find the extended state information in the
	 * memory layout. Restore just the FP/SSE and init all
	 * the other extended state.
	 */
	xrstor_state(init_xstate_buf, pcntxt_mask & ~XSTATE_FPSSE);
	return fxrstor_checking((__force struct i387_fxsave_struct *)buf);
}

/*
 * This restores directly out of user space. Exceptions are handled.
 */
int restore_i387_xstate(void __user *buf)
{
	struct task_struct *tsk = current;
	int err = 0;

	if (!buf) {
		if (used_math())
			goto clear;
		return 0;
	} else
		if (!access_ok(VERIFY_READ, buf, sig_xstate_size))
			return -EACCES;

	if (!used_math()) {
		err = init_fpu(tsk);
		if (err)
			return err;
	}

	user_fpu_begin();
	if (use_xsave())
		err = restore_user_xstate(buf);
	else
		err = fxrstor_checking((__force struct i387_fxsave_struct *)
				       buf);
	if (unlikely(err)) {
		/*
		 * Encountered an error while doing the restore from the
		 * user buffer, clear the fpu state.
		 */
clear:
		clear_fpu(tsk);
		clear_used_math();
	}
	return err;
}
#endif

/*
 * 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 size_extended = (xstate_size - sizeof(struct i387_fxsave_struct)) +
			     FP_XSTATE_MAGIC2_SIZE;

	sig_xstate_size = sizeof(struct _fpstate) + size_extended;

#ifdef CONFIG_IA32_EMULATION
	sig_xstate_ia32_size = sizeof(struct _fpstate_ia32) + size_extended;
#endif

	memset(&fx_sw_reserved, 0, sizeof(fx_sw_reserved));

	fx_sw_reserved.magic1 = FP_XSTATE_MAGIC1;
	fx_sw_reserved.extended_size = sig_xstate_size;
	fx_sw_reserved.xstate_bv = pcntxt_mask;
	fx_sw_reserved.xstate_size = xstate_size;
#ifdef CONFIG_IA32_EMULATION
	memcpy(&fx_sw_reserved_ia32, &fx_sw_reserved,
	       sizeof(struct _fpx_sw_bytes));
	fx_sw_reserved_ia32.extended_size = sig_xstate_ia32_size;
#endif
}

#ifdef CONFIG_X86_64
unsigned int sig_xstate_size = sizeof(struct _fpstate);
#endif

/*
 * 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_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;

	clts();
	/*
	 * 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);
	stts();
}

/*
 * 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);
}

/*
 * 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();
}