FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_sharedpage.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2010, 2012 Konstantin Belousov <kib@FreeBSD.org>
      * Copyright (c) 2015 The FreeBSD Foundation
      * All rights reserved.
      *
      * Portions of this software were developed by Konstantin Belousov
      * under sponsorship from the FreeBSD Foundation.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include "opt_vm.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/rwlock.h>
    #include <sys/stddef.h>
    #include <sys/sysent.h>
    #include <sys/sysctl.h>
    #include <sys/vdso.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/pmap.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_map.h>
    #include <vm/vm_object.h>
    #include <vm/vm_page.h>
    #include <vm/vm_pager.h>
    
    static struct sx shared_page_alloc_sx;
    static vm_object_t shared_page_obj;
    static int shared_page_free;
    char *shared_page_mapping;
    
    #ifdef RANDOM_FENESTRASX
    static struct vdso_fxrng_generation *fxrng_shpage_mapping;
    
    static bool fxrng_enabled = true;
    SYSCTL_BOOL(_debug, OID_AUTO, fxrng_vdso_enable, CTLFLAG_RWTUN, &fxrng_enabled,
        0, "Enable FXRNG VDSO");
    #endif
    
    void
    shared_page_write(int base, int size, const void *data)
    {
    
            bcopy(data, shared_page_mapping + base, size);
    }
    
    static int
    shared_page_alloc_locked(int size, int align)
    {
            int res;
    
            res = roundup(shared_page_free, align);
            if (res + size >= IDX_TO_OFF(shared_page_obj->size))
                    res = -1;
            else
                    shared_page_free = res + size;
            return (res);
    }
    
    int
    shared_page_alloc(int size, int align)
    {
            int res;
    
            sx_xlock(&shared_page_alloc_sx);
            res = shared_page_alloc_locked(size, align);
            sx_xunlock(&shared_page_alloc_sx);
           return (res);
   }
   
   int
   shared_page_fill(int size, int align, const void *data)
   {
           int res;
   
           sx_xlock(&shared_page_alloc_sx);
           res = shared_page_alloc_locked(size, align);
           if (res != -1)
                   shared_page_write(res, size, data);
           sx_xunlock(&shared_page_alloc_sx);
           return (res);
   }
   
   static void
   shared_page_init(void *dummy __unused)
   {
           vm_page_t m;
           vm_offset_t addr;
   
           sx_init(&shared_page_alloc_sx, "shpsx");
           shared_page_obj = vm_pager_allocate(OBJT_PHYS, 0, PAGE_SIZE,
               VM_PROT_DEFAULT, 0, NULL);
           VM_OBJECT_WLOCK(shared_page_obj);
           m = vm_page_grab(shared_page_obj, 0, VM_ALLOC_ZERO);
           VM_OBJECT_WUNLOCK(shared_page_obj);
           vm_page_valid(m);
           vm_page_xunbusy(m);
           addr = kva_alloc(PAGE_SIZE);
           pmap_qenter(addr, &m, 1);
           shared_page_mapping = (char *)addr;
   }
   
   SYSINIT(shp, SI_SUB_EXEC, SI_ORDER_FIRST, (sysinit_cfunc_t)shared_page_init,
       NULL);
   
   /*
    * Push the timehands update to the shared page.
    *
    * The lockless update scheme is similar to the one used to update the
    * in-kernel timehands, see sys/kern/kern_tc.c:tc_windup() (which
    * calls us after the timehands are updated).
    */
   static void
   timehands_update(struct vdso_sv_tk *svtk)
   {
           struct vdso_timehands th;
           struct vdso_timekeep *tk;
           uint32_t enabled, idx;
   
           enabled = tc_fill_vdso_timehands(&th);
           th.th_gen = 0;
           idx = svtk->sv_timekeep_curr;
           if (++idx >= VDSO_TH_NUM)
                   idx = 0;
           svtk->sv_timekeep_curr = idx;
           if (++svtk->sv_timekeep_gen == 0)
                   svtk->sv_timekeep_gen = 1;
   
           tk = (struct vdso_timekeep *)(shared_page_mapping +
               svtk->sv_timekeep_off);
           tk->tk_th[idx].th_gen = 0;
           atomic_thread_fence_rel();
           if (enabled)
                   tk->tk_th[idx] = th;
           atomic_store_rel_32(&tk->tk_th[idx].th_gen, svtk->sv_timekeep_gen);
           atomic_store_rel_32(&tk->tk_current, idx);
   
           /*
            * The ordering of the assignment to tk_enabled relative to
            * the update of the vdso_timehands is not important.
            */
           tk->tk_enabled = enabled;
   }
   
   #ifdef COMPAT_FREEBSD32
   static void
   timehands_update32(struct vdso_sv_tk *svtk)
   {
           struct vdso_timehands32 th;
           struct vdso_timekeep32 *tk;
           uint32_t enabled, idx;
   
           enabled = tc_fill_vdso_timehands32(&th);
           th.th_gen = 0;
           idx = svtk->sv_timekeep_curr;
           if (++idx >= VDSO_TH_NUM)
                   idx = 0;
           svtk->sv_timekeep_curr = idx;
           if (++svtk->sv_timekeep_gen == 0)
                   svtk->sv_timekeep_gen = 1;
   
           tk = (struct vdso_timekeep32 *)(shared_page_mapping +
               svtk->sv_timekeep_off);
           tk->tk_th[idx].th_gen = 0;
           atomic_thread_fence_rel();
           if (enabled)
                   tk->tk_th[idx] = th;
           atomic_store_rel_32(&tk->tk_th[idx].th_gen, svtk->sv_timekeep_gen);
           atomic_store_rel_32(&tk->tk_current, idx);
           tk->tk_enabled = enabled;
   }
   #endif
   
   /*
    * This is hackish, but easiest way to avoid creating list structures
    * that needs to be iterated over from the hardclock interrupt
    * context.
    */
   static struct vdso_sv_tk *host_svtk;
   #ifdef COMPAT_FREEBSD32
   static struct vdso_sv_tk *compat32_svtk;
   #endif
   
   void
   timekeep_push_vdso(void)
   {
   
           if (host_svtk != NULL)
                   timehands_update(host_svtk);
   #ifdef COMPAT_FREEBSD32
           if (compat32_svtk != NULL)
                   timehands_update32(compat32_svtk);
   #endif
   }
   
   struct vdso_sv_tk *
   alloc_sv_tk(void)
   {
           struct vdso_sv_tk *svtk;
           int tk_base;
           uint32_t tk_ver;
   
           tk_ver = VDSO_TK_VER_CURR;
           svtk = malloc(sizeof(struct vdso_sv_tk), M_TEMP, M_WAITOK | M_ZERO);
           tk_base = shared_page_alloc(sizeof(struct vdso_timekeep) +
               sizeof(struct vdso_timehands) * VDSO_TH_NUM, 16);
           KASSERT(tk_base != -1, ("tk_base -1 for native"));
           shared_page_write(tk_base + offsetof(struct vdso_timekeep, tk_ver),
               sizeof(uint32_t), &tk_ver);
           svtk->sv_timekeep_off = tk_base;
           timekeep_push_vdso();
           return (svtk);
   }
   
   #ifdef COMPAT_FREEBSD32
   struct vdso_sv_tk *
   alloc_sv_tk_compat32(void)
   {
           struct vdso_sv_tk *svtk;
           int tk_base;
           uint32_t tk_ver;
   
           svtk = malloc(sizeof(struct vdso_sv_tk), M_TEMP, M_WAITOK | M_ZERO);
           tk_ver = VDSO_TK_VER_CURR;
           tk_base = shared_page_alloc(sizeof(struct vdso_timekeep32) +
               sizeof(struct vdso_timehands32) * VDSO_TH_NUM, 16);
           KASSERT(tk_base != -1, ("tk_base -1 for 32bit"));
           shared_page_write(tk_base + offsetof(struct vdso_timekeep32,
               tk_ver), sizeof(uint32_t), &tk_ver);
           svtk->sv_timekeep_off = tk_base;
           timekeep_push_vdso();
           return (svtk);
   }
   #endif
   
   #ifdef RANDOM_FENESTRASX
   void
   fxrng_push_seed_generation(uint64_t gen)
   {
           if (fxrng_shpage_mapping == NULL || !fxrng_enabled)
                   return;
           KASSERT(gen < INT32_MAX,
               ("fxrng seed version shouldn't roll over a 32-bit counter "
                "for approximately 456,000 years"));
           atomic_store_rel_32(&fxrng_shpage_mapping->fx_generation32,
               (uint32_t)gen);
   }
   
   static void
   alloc_sv_fxrng_generation(void)
   {
           int base;
   
           /*
            * Allocate a full cache line for the fxrng root generation (64-bit
            * counter, or truncated 32-bit counter on ILP32 userspace).  It is
            * important that the line is not shared with frequently dirtied data,
            * and the shared page allocator lacks a __read_mostly mechanism.
            * However, PAGE_SIZE is typically large relative to the amount of
            * stuff we've got in it so far, so maybe the possible waste isn't an
            * issue.
            */
           base = shared_page_alloc(CACHE_LINE_SIZE, CACHE_LINE_SIZE);
           KASSERT(base != -1, ("%s: base allocation failed", __func__));
           fxrng_shpage_mapping = (void *)(shared_page_mapping + base);
           *fxrng_shpage_mapping = (struct vdso_fxrng_generation) {
                   .fx_vdso_version = VDSO_FXRNG_VER_CURR,
           };
   }
   #endif /* RANDOM_FENESTRASX */
   
   void
   exec_sysvec_init(void *param)
   {
           struct sysentvec *sv;
   #ifdef RANDOM_FENESTRASX
           ptrdiff_t base;
   #endif
   
           sv = (struct sysentvec *)param;
           if ((sv->sv_flags & SV_SHP) == 0)
                   return;
           sv->sv_shared_page_obj = shared_page_obj;
           sv->sv_sigcode_base = sv->sv_shared_page_base +
               shared_page_fill(*(sv->sv_szsigcode), 16, sv->sv_sigcode);
           if ((sv->sv_flags & SV_ABI_MASK) != SV_ABI_FREEBSD)
                   return;
           if ((sv->sv_flags & SV_TIMEKEEP) != 0) {
   #ifdef COMPAT_FREEBSD32
                   if ((sv->sv_flags & SV_ILP32) != 0) {
                           KASSERT(compat32_svtk == NULL,
                               ("Compat32 already registered"));
                           compat32_svtk = alloc_sv_tk_compat32();
                           sv->sv_timekeep_base = sv->sv_shared_page_base +
                               compat32_svtk->sv_timekeep_off;
                   } else {
   #endif
                           KASSERT(host_svtk == NULL, ("Host already registered"));
                           host_svtk = alloc_sv_tk();
                           sv->sv_timekeep_base = sv->sv_shared_page_base +
                               host_svtk->sv_timekeep_off;
   #ifdef COMPAT_FREEBSD32
                   }
   #endif
           }
   #ifdef RANDOM_FENESTRASX
           if ((sv->sv_flags & SV_RNG_SEED_VER) != 0) {
                   /*
                    * Only allocate a single VDSO entry for multiple sysentvecs,
                    * i.e., native and COMPAT32.
                    */
                   if (fxrng_shpage_mapping == NULL)
                           alloc_sv_fxrng_generation();
                   base = (char *)fxrng_shpage_mapping - shared_page_mapping;
                   sv->sv_fxrng_gen_base = sv->sv_shared_page_base + base;
           }
   #endif
   }
   
   void
   exec_sysvec_init_secondary(struct sysentvec *sv, struct sysentvec *sv2)
   {
           MPASS((sv2->sv_flags & SV_ABI_MASK) == (sv->sv_flags & SV_ABI_MASK));
           MPASS((sv2->sv_flags & SV_TIMEKEEP) == (sv->sv_flags & SV_TIMEKEEP));
           MPASS((sv2->sv_flags & SV_SHP) != 0 && (sv->sv_flags & SV_SHP) != 0);
           MPASS((sv2->sv_flags & SV_RNG_SEED_VER) ==
               (sv->sv_flags & SV_RNG_SEED_VER));
   
           sv2->sv_shared_page_obj = sv->sv_shared_page_obj;
           sv2->sv_sigcode_base = sv2->sv_shared_page_base +
               (sv->sv_sigcode_base - sv->sv_shared_page_base);
           if ((sv2->sv_flags & SV_ABI_MASK) != SV_ABI_FREEBSD)
                   return;
           if ((sv2->sv_flags & SV_TIMEKEEP) != 0) {
                   sv2->sv_timekeep_base = sv2->sv_shared_page_base +
                       (sv->sv_timekeep_base - sv->sv_shared_page_base);
           }
           if ((sv2->sv_flags & SV_RNG_SEED_VER) != 0) {
                   sv2->sv_fxrng_gen_base = sv2->sv_shared_page_base +
                       (sv->sv_fxrng_gen_base - sv->sv_shared_page_base);
           }
   }

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