git: 90049eabcfad - main - vm_map_protect(): add VM_MAP_PROTECT_GROWSDOWN flag

[Konstantin Belousov]

The branch main has been updated by kib:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=90049eabcfadf229e3983f04310a8ea28fe3d2b1

commit 90049eabcfadf229e3983f04310a8ea28fe3d2b1
Author:     Konstantin Belousov <k...@freebsd.org>
AuthorDate: 2023-07-28 00:40:53 +0000
Commit:     Konstantin Belousov <k...@freebsd.org>
CommitDate: 2023-08-12 06:28:14 +0000

    vm_map_protect(): add VM_MAP_PROTECT_GROWSDOWN flag
    
    which requests to propagate lowest stack segment protection to the grow gap.
    This seems to be required for Linux emulation.
    
    Reported by:    dchagin
    Reviewed by:    alc, markj
    Tested by:      pho
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Differential revision:  https://reviews.freebsd.org/D41099
---
 sys/vm/vm_map.c | 19 +++++++++++++++++++
 sys/vm/vm_map.h |  1 +
 2 files changed, 20 insertions(+)

diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
index 1c806d6cae34..8d98af7709cd 100644
--- a/sys/vm/vm_map.c
+++ b/sys/vm/vm_map.c
@@ -2758,6 +2758,7 @@ vm_map_protect(vm_map_t map, vm_offset_t start, 
vm_offset_t end,
        vm_map_entry_t entry, first_entry, in_tran, prev_entry;
        vm_object_t obj;
        struct ucred *cred;
+       vm_offset_t orig_start;
        vm_prot_t check_prot, max_prot, old_prot;
        int rv;
 
@@ -2769,8 +2770,10 @@ vm_map_protect(vm_map_t map, vm_offset_t start, 
vm_offset_t end,
            !CONTAINS_BITS(new_maxprot, new_prot))
                return (KERN_OUT_OF_BOUNDS);
 
+       orig_start = start;
 again:
        in_tran = NULL;
+       start = orig_start;
        vm_map_lock(map);
 
        if ((map->flags & MAP_WXORX) != 0 &&
@@ -2793,6 +2796,22 @@ again:
        if (!vm_map_lookup_entry(map, start, &first_entry))
                first_entry = vm_map_entry_succ(first_entry);
 
+       if ((flags & VM_MAP_PROTECT_GROWSDOWN) != 0 &&
+           (first_entry->eflags & MAP_ENTRY_GROWS_DOWN) != 0) {
+               /*
+                * Handle Linux's PROT_GROWSDOWN flag.
+                * It means that protection is applied down to the
+                * whole stack, including the specified range of the
+                * mapped region, and the grow down region (AKA
+                * guard).
+                */
+               while (!CONTAINS_BITS(first_entry->eflags,
+                   MAP_ENTRY_GUARD | MAP_ENTRY_STACK_GAP_DN) &&
+                   first_entry != vm_map_entry_first(map))
+                       first_entry = vm_map_entry_pred(first_entry);
+               start = first_entry->start;
+       }
+
        /*
         * Make a first pass to check for protection violations.
         */
diff --git a/sys/vm/vm_map.h b/sys/vm/vm_map.h
index 08bc6532b8b8..e41516477af4 100644
--- a/sys/vm/vm_map.h
+++ b/sys/vm/vm_map.h
@@ -522,6 +522,7 @@ vm_map_entry_succ(vm_map_entry_t entry)
 
 #define        VM_MAP_PROTECT_SET_PROT         0x0001
 #define        VM_MAP_PROTECT_SET_MAXPROT      0x0002
+#define        VM_MAP_PROTECT_GROWSDOWN        0x0004
 
 int vm_map_protect(vm_map_t map, vm_offset_t start, vm_offset_t end,
     vm_prot_t new_prot, vm_prot_t new_maxprot, int flags);