Ivan A. Melnikov <i...@altlinux.org> writes:
> While pgd_find_hole_fallback returns the beginning of the > hole found, pgb_find_hole returns guest_base, which > is somewhat different as the binary qemu-user is loading > usually has non-zero load address. > > Failing to take this into account leads to random crashes > if the hole is "just big enough", but not bigger: > in that case, important mappings (e.g. parts of qemu-user > itself) may be replaced with the binary it is loading > (e.g. the guest elf interpreter). > > This patch also fixes the return type of pgd_find_hole_fallback: > it returns -1 if no hole is found, so a signed return type > should be used. I don't think it should. For one thing the type is preserved as uintptr_t all the way up the call chain so just changing it here doesn't help much. -1 is really just a quick way of saying all bits are set which is the one "fail" value we check for. The address space is big enough we could theoretically return a chunk of space that otherwise has the top bit set. > > Downstream issue (in Russian): https://bugzilla.altlinux.org/39141 > Signed-off-by: Ivan A. Melnikov <i...@altlinux.org> > --- > linux-user/elfload.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/linux-user/elfload.c b/linux-user/elfload.c > index bab4237e90..acd510532c 100644 > --- a/linux-user/elfload.c > +++ b/linux-user/elfload.c > @@ -2205,9 +2205,11 @@ static void pgb_have_guest_base(const char > *image_name, abi_ulong guest_loaddr, > * /proc/self/map. It can potentially take a very long time as we can > * only dumbly iterate up the host address space seeing if the > * allocation would work. > + * > + * Returns the start addres of the hole found, or -1 if no hole found. > */ > -static uintptr_t pgd_find_hole_fallback(uintptr_t guest_size, uintptr_t brk, > - long align, uintptr_t offset) > +static intptr_t pgd_find_hole_fallback(uintptr_t guest_size, uintptr_t brk, > + long align, uintptr_t offset) > { > uintptr_t base; > > @@ -2235,7 +2237,7 @@ static uintptr_t pgd_find_hole_fallback(uintptr_t > guest_size, uintptr_t brk, > munmap((void *) align_start, guest_size); > if (MAP_FIXED_NOREPLACE != 0 || > mmap_start == (void *) align_start) { > - return (uintptr_t) mmap_start + offset; > + return (intptr_t) mmap_start + offset; > } > } > base += qemu_host_page_size; > @@ -2259,7 +2261,8 @@ 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 > guest_loaddr) ? (ret - guest_loaddr) : -1; So I think we just want: return ret == -1 ? -1 : (ret - guest_loaddr); do we have a test case that triggers this? > } > > /* The first hole is before the first map entry. */ -- Alex Bennée
