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linux-user/elfload: fix address calculation in fallback scenario 

Previously, guest_loaddr was not taken into account when returning an
address from pgb_find_hole when /proc/self/maps was unavailable which
caused an improper guest_base address to be calculated.

This could cause a SIGSEGV later in load_elf_image -> target_mmap for
ET_EXEC type images since the mmap MAP_FIXED flag is specified which
could clobber existing mappings at the address returnd by g2h().

  mmap(0xd87000, 16846912, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE|0x100000, -1, 0) = 0xd87000
  munmap(0xd87000, 16846912)              = 0
  write(2, "Locating guest address space @ 0"..., 40Locating guest address space @ 0xd87000) = 40
  mmap(0x1187000, 16850944, PROT_NONE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS|MAP_NORESERVE, -1, 0) = 0x1187000
  --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_ACCERR, si_addr=0x2188310} ---
  +++ killed by SIGSEGV +++

Now, pgd_find_hole accounts for guest_loaddr in this scenario.

Fixes: ad592e37df ("linux-user: provide fallback pgd_find_hole for bare chroots")
Signed-off-by: Vincent Fazio <vfazio@gmail.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210131061948.15990-1-vfazio@xes-inc.com>
[lv: updated it to check if ret == -1]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
This commit is contained in:
Vincent Fazio 2021-01-31 00:19:48 -06:00 committed by Laurent Vivier
parent 934eed5178
commit 0266e8e3b3
1 changed files with 2 additions and 1 deletions
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linux-user/elfload.c
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@ -2235,7 +2235,8 @@ static uintptr_t pgb_find_hole(uintptr_t guest_loaddr, uintptr_t guest_size,
brk = (uintptr_t)sbrk(0);
if (!maps) {
return pgd_find_hole_fallback(guest_size, brk, align, offset);
ret = pgd_find_hole_fallback(guest_size, brk, align, offset);
return ret == -1 ? -1 : ret - guest_loaddr;
}
/* The first hole is before the first map entry. */