mcontext.c

// SPDX-License-Identifier: GPL-2.0
#define __FRAME_OFFSETS
#include <linux/errno.h>
#include <linux/string.h>
#include <sys/ucontext.h>
#include <asm/ptrace.h>
#include <asm/sigcontext.h>
#include <sysdep/ptrace.h>
#include <sysdep/mcontext.h>
#include <arch.h>

void get_regs_from_mc(struct uml_pt_regs *regs, mcontext_t *mc)
{
#ifdef __i386__
#define COPY2(X,Y) regs->gp[X] = mc->gregs[REG_##Y]
#define COPY(X) regs->gp[X] = mc->gregs[REG_##X]
#define COPY_SEG(X) regs->gp[X] = mc->gregs[REG_##X] & 0xffff;
#define COPY_SEG_CPL3(X) regs->gp[X] = (mc->gregs[REG_##X] & 0xffff) | 3;
	COPY_SEG(GS); COPY_SEG(FS); COPY_SEG(ES); COPY_SEG(DS);
	COPY(EDI); COPY(ESI); COPY(EBP);
	COPY2(UESP, ESP); /* sic */
	COPY(EBX); COPY(EDX); COPY(ECX); COPY(EAX);
	COPY(EIP); COPY_SEG_CPL3(CS); COPY(EFL); COPY_SEG_CPL3(SS);
#undef COPY2
#undef COPY
#undef COPY_SEG
#undef COPY_SEG_CPL3
#else
#define COPY2(X,Y) regs->gp[X/sizeof(unsigned long)] = mc->gregs[REG_##Y]
#define COPY(X) regs->gp[X/sizeof(unsigned long)] = mc->gregs[REG_##X]
	COPY(R8); COPY(R9); COPY(R10); COPY(R11);
	COPY(R12); COPY(R13); COPY(R14); COPY(R15);
	COPY(RDI); COPY(RSI); COPY(RBP); COPY(RBX);
	COPY(RDX); COPY(RAX); COPY(RCX); COPY(RSP);
	COPY(RIP);
	COPY2(EFLAGS, EFL);
	COPY2(CS, CSGSFS);
	regs->gp[SS / sizeof(unsigned long)] = mc->gregs[REG_CSGSFS] >> 48;
#undef COPY2
#undef COPY
#endif
}

void mc_set_rip(void *_mc, void *target)
{
	mcontext_t *mc = _mc;

#ifdef __i386__
	mc->gregs[REG_EIP] = (unsigned long)target;
#else
	mc->gregs[REG_RIP] = (unsigned long)target;
#endif
}

/* Same thing, but the copy macros are turned around. */
void get_mc_from_regs(struct uml_pt_regs *regs, mcontext_t *mc, int single_stepping)
{
#ifdef __i386__
#define COPY2(X,Y) mc->gregs[REG_##Y] = regs->gp[X]
#define COPY(X) mc->gregs[REG_##X] = regs->gp[X]
#define COPY_SEG(X) mc->gregs[REG_##X] = regs->gp[X] & 0xffff;
#define COPY_SEG_CPL3(X) mc->gregs[REG_##X] = (regs->gp[X] & 0xffff) | 3;
	COPY_SEG(GS); COPY_SEG(FS); COPY_SEG(ES); COPY_SEG(DS);
	COPY(EDI); COPY(ESI); COPY(EBP);
	COPY2(UESP, ESP); /* sic */
	COPY(EBX); COPY(EDX); COPY(ECX); COPY(EAX);
	COPY(EIP); COPY_SEG_CPL3(CS); COPY(EFL); COPY_SEG_CPL3(SS);
#else
#define COPY2(X,Y) mc->gregs[REG_##Y] = regs->gp[X/sizeof(unsigned long)]
#define COPY(X) mc->gregs[REG_##X] = regs->gp[X/sizeof(unsigned long)]
	COPY(R8); COPY(R9); COPY(R10); COPY(R11);
	COPY(R12); COPY(R13); COPY(R14); COPY(R15);
	COPY(RDI); COPY(RSI); COPY(RBP); COPY(RBX);
	COPY(RDX); COPY(RAX); COPY(RCX); COPY(RSP);
	COPY(RIP);
	COPY2(EFLAGS, EFL);
	mc->gregs[REG_CSGSFS] = mc->gregs[REG_CSGSFS] & 0xffffffffffffl;
	mc->gregs[REG_CSGSFS] |= (regs->gp[SS / sizeof(unsigned long)] & 0xffff) << 48;
#endif

	if (single_stepping)
		mc->gregs[REG_EFL] |= X86_EFLAGS_TF;
	else
		mc->gregs[REG_EFL] &= ~X86_EFLAGS_TF;
}

#ifdef CONFIG_X86_32
struct _xstate_64 {
	struct _fpstate_64		fpstate;
	struct _header			xstate_hdr;
	struct _ymmh_state		ymmh;
	/* New processor state extensions go here: */
};

/* Not quite the right structures as these contain more information */
int um_i387_from_fxsr(struct _fpstate_32 *i387,
		      const struct _fpstate_64 *fxsave);
int um_fxsr_from_i387(struct _fpstate_64 *fxsave,
		      const struct _fpstate_32 *from);
#else
#define _xstate_64 _xstate
#endif

static struct _fpstate *get_fpstate(struct stub_data *data,
				    mcontext_t *mcontext,
				    int *fp_size)
{
	struct _fpstate *res;

	/* Assume floating point registers are on the same page */
	res = (void *)(((unsigned long)mcontext->fpregs &
			(UM_KERN_PAGE_SIZE - 1)) +
		       (unsigned long)&data->sigstack[0]);

	if ((void *)res + sizeof(struct _fpstate) >
	    (void *)data->sigstack + sizeof(data->sigstack))
		return NULL;

	if (res->sw_reserved.magic1 != FP_XSTATE_MAGIC1) {
		*fp_size = sizeof(struct _fpstate);
	} else {
		char *magic2_addr;

		magic2_addr = (void *)res;
		magic2_addr += res->sw_reserved.extended_size;
		magic2_addr -= FP_XSTATE_MAGIC2_SIZE;

		/* We still need to be within our stack */
		if ((void *)magic2_addr >
		    (void *)data->sigstack + sizeof(data->sigstack))
			return NULL;

		/* If we do not read MAGIC2, then we did something wrong */
		if (*(__u32 *)magic2_addr != FP_XSTATE_MAGIC2)
			return NULL;

		/* Remove MAGIC2 from the size, we do not save/restore it */
		*fp_size = res->sw_reserved.extended_size -
			   FP_XSTATE_MAGIC2_SIZE;
	}

	return res;
}

int get_stub_state(struct uml_pt_regs *regs, struct stub_data *data,
		   unsigned long *fp_size_out)
{
	mcontext_t *mcontext;
	struct _fpstate *fpstate_stub;
	struct _xstate_64 *xstate_stub;
	int fp_size, xstate_size;

	/* mctx_offset is verified by wait_stub_done_seccomp */
	mcontext = (void *)&data->sigstack[data->mctx_offset];

	get_regs_from_mc(regs, mcontext);

	fpstate_stub = get_fpstate(data, mcontext, &fp_size);
	if (!fpstate_stub)
		return -EINVAL;

#ifdef CONFIG_X86_32
	xstate_stub = (void *)&fpstate_stub->_fxsr_env;
	xstate_size = fp_size - offsetof(struct _fpstate_32, _fxsr_env);
#else
	xstate_stub = (void *)fpstate_stub;
	xstate_size = fp_size;
#endif

	if (fp_size_out)
		*fp_size_out = xstate_size;

	if (xstate_size > host_fp_size)
		return -ENOSPC;

	memcpy(&regs->fp, xstate_stub, xstate_size);

	/* We do not need to read the x86_64 FS_BASE/GS_BASE registers as
	 * we do not permit userspace to set them directly.
	 */

#ifdef CONFIG_X86_32
	/* Read the i387 legacy FP registers */
	if (um_fxsr_from_i387((void *)&regs->fp, fpstate_stub))
		return -EINVAL;
#endif

	return 0;
}

/* Copied because we cannot include regset.h here. */
struct task_struct;
struct user_regset;
struct membuf {
	void *p;
	size_t left;
};

int fpregs_legacy_get(struct task_struct *target,
		      const struct user_regset *regset,
		      struct membuf to);

int set_stub_state(struct uml_pt_regs *regs, struct stub_data *data,
		   int single_stepping)
{
	mcontext_t *mcontext;
	struct _fpstate *fpstate_stub;
	struct _xstate_64 *xstate_stub;
	int fp_size, xstate_size;

	/* mctx_offset is verified by wait_stub_done_seccomp */
	mcontext = (void *)&data->sigstack[data->mctx_offset];

	if ((unsigned long)mcontext < (unsigned long)data->sigstack ||
	    (unsigned long)mcontext >
			(unsigned long) data->sigstack +
			sizeof(data->sigstack) - sizeof(*mcontext))
		return -EINVAL;

	get_mc_from_regs(regs, mcontext, single_stepping);

	fpstate_stub = get_fpstate(data, mcontext, &fp_size);
	if (!fpstate_stub)
		return -EINVAL;

#ifdef CONFIG_X86_32
	xstate_stub = (void *)&fpstate_stub->_fxsr_env;
	xstate_size = fp_size - offsetof(struct _fpstate_32, _fxsr_env);
#else
	xstate_stub = (void *)fpstate_stub;
	xstate_size = fp_size;
#endif

	memcpy(xstate_stub, &regs->fp, xstate_size);

#ifdef __i386__
	/*
	 * On x86, the GDT entries are updated by arch_set_tls.
	 */

	/* Store the i387 legacy FP registers which the host will use */
	if (um_i387_from_fxsr(fpstate_stub, (void *)&regs->fp))
		return -EINVAL;
#else
	/*
	 * On x86_64, we need to sync the FS_BASE/GS_BASE registers using the
	 * arch specific data.
	 */
	if (data->arch_data.fs_base != regs->gp[FS_BASE / sizeof(unsigned long)]) {
		data->arch_data.fs_base = regs->gp[FS_BASE / sizeof(unsigned long)];
		data->arch_data.sync |= STUB_SYNC_FS_BASE;
	}
	if (data->arch_data.gs_base != regs->gp[GS_BASE / sizeof(unsigned long)]) {
		data->arch_data.gs_base = regs->gp[GS_BASE / sizeof(unsigned long)];
		data->arch_data.sync |= STUB_SYNC_GS_BASE;
	}
#endif

	return 0;
}