Been a couple weeks, checking to see if anyone has looked at this. On Sat, May 2, 2020 at 5:43 PM Jonathan Marler <johnnymar...@gmail.com> wrote:
> FYI, I applied this patch to the qemu build that zig uses to run > non-native tests ( > https://github.com/ziglang/qemu-static/blob/master/patch/mremap-underflow.diff > ) > > After applying it, my new code that calls mremap now passes, > whereas before the fix I was getting a segfault. > > On Sat, May 2, 2020 at 10:12 AM Jonathan Marler <johnnymar...@gmail.com> > wrote: > >> Fixes: https://bugs.launchpad.net/bugs/1876373 >> >> This code path in mmap occurs when a page size is decreased with mremap. >> When a section of pages is shrunk, qemu calls mmap_reserve on the pages >> that were released. However, it has the diff operation reversed, >> subtracting the larger old_size from the smaller new_size. Instead, it >> should be subtracting the smaller new_size from the larger old_size. You >> can also see in the previous line of the change that this mmap_reserve call >> only occurs when old_size > new_size. >> >> Signed-off-by: Jonathan Marler <johnnymar...@gmail.com> >> --- >> linux-user/mmap.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/linux-user/mmap.c b/linux-user/mmap.c >> index e378033797..caab62909e 100644 >> --- a/linux-user/mmap.c >> +++ b/linux-user/mmap.c >> @@ -708,7 +708,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong >> old_size, >> if (prot == 0) { >> host_addr = mremap(g2h(old_addr), old_size, new_size, flags); >> if (host_addr != MAP_FAILED && reserved_va && old_size > >> new_size) { >> - mmap_reserve(old_addr + old_size, new_size - old_size); >> + mmap_reserve(old_addr + old_size, old_size - new_size); >> } >> } else { >> errno = ENOMEM; >> -- >> 2.23.1 >> >>
