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/* Create new context.
Copyright (C) 2002-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <sysdep.h>
#include <stdarg.h>
#include <stdint.h>
#include <stdlib.h>
#include <ucontext.h>
#include <sys/mman.h>
#define GCS_MAGIC 0x47435300
static struct _aarch64_ctx *extension (void *p)
{
return p;
}
struct gcs_list {
struct gcs_list *next;
void *base;
size_t size;
};
static __thread struct gcs_list *gcs_list_head = NULL;
static void
record_gcs (void *base, size_t size)
{
struct gcs_list *p = malloc (sizeof *p);
if (p == NULL)
abort ();
p->base = base;
p->size = size;
p->next = gcs_list_head;
gcs_list_head = p;
}
static void
free_gcs_list (void)
{
for (;;)
{
struct gcs_list *p = gcs_list_head;
if (p == NULL)
break;
gcs_list_head = p->next;
__munmap (p->base, p->size);
free (p);
}
}
/* Called during thread shutdown to free resources. */
void
__libc_aarch64_thread_freeres (void)
{
free_gcs_list ();
}
#ifndef __NR_map_shadow_stack
# define __NR_map_shadow_stack 453
#endif
#ifndef SHADOW_STACK_SET_TOKEN
# define SHADOW_STACK_SET_TOKEN (1UL << 0)
# define SHADOW_STACK_SET_MARKER (1UL << 1)
#endif
static void *
map_shadow_stack (void *addr, size_t size, unsigned long flags)
{
return (void *) INLINE_SYSCALL_CALL (map_shadow_stack, addr, size, flags);
}
#define GCS_MAX_SIZE (1UL << 31)
#define GCS_ALTSTACK_RESERVE 160
static void *
alloc_makecontext_gcs (size_t stack_size)
{
size_t size = (stack_size / 2 + GCS_ALTSTACK_RESERVE) & -8UL;
if (size > GCS_MAX_SIZE)
size = GCS_MAX_SIZE;
unsigned long flags = SHADOW_STACK_SET_MARKER | SHADOW_STACK_SET_TOKEN;
void *base = map_shadow_stack (NULL, size, flags);
if (base == (void *) -1)
/* ENOSYS, bad size or OOM. */
abort ();
record_gcs (base, size);
uint64_t *gcsp = (uint64_t *) ((char *) base + size);
/* Skip end of GCS token. */
gcsp--;
/* Verify GCS cap token. */
gcsp--;
if (((uint64_t)gcsp & 0xfffffffffffff000) + 1 != *gcsp)
abort ();
/* Return the target GCS pointer for context switch. */
return gcsp + 1;
}
void
__free_makecontext_gcs (void *gcs)
{
struct gcs_list *p = gcs_list_head;
struct gcs_list **q = &gcs_list_head;
for (;;)
{
if (p == NULL)
abort ();
if (gcs == p->base + p->size - 8)
break;
q = &p->next;
p = p->next;
}
*q = p->next;
__munmap (p->base, p->size);
free (p);
}
/* makecontext sets up a stack and the registers for the
user context. The stack looks like this:
+-----------------------+
| padding as required |
+-----------------------+
sp -> | parameter 7-n |
+-----------------------+
The registers are set up like this:
%x0 .. %x7: parameter 1 to 8
%x19 : uc_link
%sp : stack pointer.
*/
void
__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
{
extern void __startcontext (void);
uint64_t *sp;
va_list ap;
int i;
sp = (uint64_t *)
((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
/* Allocate stack arguments. */
sp -= argc < 8 ? 0 : argc - 8;
/* Keep the stack aligned. */
sp = (uint64_t *) (((uintptr_t) sp) & -16L);
ucp->uc_mcontext.regs[19] = (uintptr_t) ucp->uc_link;
ucp->uc_mcontext.regs[20] = (uintptr_t) func;
ucp->uc_mcontext.sp = (uintptr_t) sp;
ucp->uc_mcontext.pc = (uintptr_t) __startcontext;
ucp->uc_mcontext.regs[29] = (uintptr_t) 0;
ucp->uc_mcontext.regs[30] = (uintptr_t) 0;
void *p = ucp->uc_mcontext.__reserved;
if (extension (p)->magic == FPSIMD_MAGIC)
p = (char *)p + extension (p)->size;
if (extension (p)->magic == GCS_MAGIC)
{
/* Using the kernel struct gcs_context layout. */
struct { uint64_t x, gcspr, y, z; } *q = p;
q->gcspr = (uint64_t) alloc_makecontext_gcs (ucp->uc_stack.ss_size);
}
va_start (ap, argc);
for (i = 0; i < argc; ++i)
if (i < 8)
ucp->uc_mcontext.regs[i] = va_arg (ap, uint64_t);
else
sp[i - 8] = va_arg (ap, uint64_t);
va_end (ap);
}
weak_alias (__makecontext, makecontext)
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