Re: git: 50d663b14b31 - main - vm: Fix vm_map_find_min()

[Alan Cox]

I see.  That change fixed the case where the address hint is non-zero, 
e.g., 0x100000, but not zero.

On 7/30/23 05:58, Dmitry Chagin wrote:
On Sun, Jul 30, 2023 at 01:30:37PM +0300, Dmitry Chagin wrote:
On Wed, Jul 26, 2023 at 05:25:37AM +0000, Alan Cox wrote:
The branch main has been updated by alc:
URL: 
https://urldefense.com/v3/__https://cgit.FreeBSD.org/src/commit/?id=50d663b14b310d6020b4b6cc92d4fae985f086f2__;!!BuQPrrmRaQ!mJGmkdRJ06TT6ocFnVe7lPS7hSNIIhrCQH9IKMbB6XZVJuiUc2_wPJ55o1zzD6AhClmQwgQKHvKnW4rs75yVrtax$

commit 50d663b14b310d6020b4b6cc92d4fae985f086f2
Author:     Alan Cox <a...@freebsd.org>
AuthorDate: 2023-07-25 07:24:19 +0000
Commit:     Alan Cox <a...@freebsd.org>
CommitDate: 2023-07-26 05:24:50 +0000

     vm: Fix vm_map_find_min()
     
     Fix the handling of address hints that are less than min_addr by
     vm_map_find_min().
     
Thank you for fixing that, however it still fails under Linuxulator.


#include <sys/mman.h>
#include <sys/stat.h>

#include <assert.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main(int argc, char** argv)
{
        struct stat sb;
        void *s32;
        int f, r;

        f = open(argv[0], O_RDONLY);
        assert(f > 0);

        r = fstat(f, &sb);
        assert(r == 0);

        s32  = mmap(NULL, sb.st_size, PROT_READ,
            MAP_32BIT|MAP_PRIVATE, f, 0);
        assert(s32 != MAP_FAILED);
        assert((uintptr_t)s32 < 0x80000000);

        close(f);
        munmap(s32, sb.st_size);
        return (0);
}

hmm, it also fails natively with disable aslr



     Reported by:    dchagin
     Reviewed by:    kib
     Fixes:  d8e6f4946cec0 "vm: Fix anonymous memory clustering under ASLR"
     Differential Revision:  
https://urldefense.com/v3/__https://reviews.freebsd.org/D41159__;!!BuQPrrmRaQ!mJGmkdRJ06TT6ocFnVe7lPS7hSNIIhrCQH9IKMbB6XZVJuiUc2_wPJ55o1zzD6AhClmQwgQKHvKnW4rs70ygLqzX$
---
  sys/vm/vm_map.c | 4 ++--
  1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sys/vm/vm_map.c b/sys/vm/vm_map.c
index 444e09986d4e..eb607d519247 100644
--- a/sys/vm/vm_map.c
+++ b/sys/vm/vm_map.c
@@ -2255,10 +2255,10 @@ vm_map_find_min(vm_map_t map, vm_object_t object, 
vm_ooffset_t offset,
        int rv;
  
  	hint = *addr;
-       if (hint == 0)
+       if (hint == 0) {
                cow |= MAP_NO_HINT;
-       if (hint < min_addr)
                *addr = hint = min_addr;
+       }
        for (;;) {
                rv = vm_map_find(map, object, offset, addr, length, max_addr,
                    find_space, prot, max, cow);