On kernel 5.7 and later, kallsyms_lookup_name() can no longer be called from a kernel
module for reasons described here: https://lwn.net/Articles/813350/
As binder really needs to use kallsysms_lookup_name() to access some kernel
functions that otherwise wouldn't be accessible, KProbes are used on later
kernels to get the address of kallsysms_lookup_name(). The function is
afterwards used just as before. This is a very dirty hack though and the much
better solution would be if all the functions that are currently resolved
with kallsysms_lookup_name() would get an EXPORT_SYMBOL() annotation to
make them directly accessible to kernel modules.
Amit Pundir and Youling in parallel reported crashes with recent
mainline kernels running Android:
F DEBUG : *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
F DEBUG : Build fingerprint: 'Android/db410c32_only/db410c32_only:Q/OC-MR1/102:userdebug/test-key
F DEBUG : Revision: '0'
F DEBUG : ABI: 'arm'
F DEBUG : pid: 2261, tid: 2261, name: zygote >>> zygote <<<
F DEBUG : signal 7 (SIGBUS), code 2 (BUS_ADRERR), fault addr 0xec00008
... <snip> ...
F DEBUG : backtrace:
F DEBUG : #00 pc 00001c04 /system/lib/libc.so (memset+48)
F DEBUG : #01 pc 0010c513 /system/lib/libart.so (create_mspace_with_base+82)
F DEBUG : #02 pc 0015c601 /system/lib/libart.so (art::gc::space::DlMallocSpace::CreateMspace(void*, unsigned int, unsigned int)+40)
F DEBUG : #03 pc 0015c3ed /system/lib/libart.so (art::gc::space::DlMallocSpace::CreateFromMemMap(art::MemMap*, std::__1::basic_string<char, std::__ 1::char_traits<char>, std::__1::allocator<char>> const&, unsigned int, unsigned int, unsigned int, unsigned int, bool)+36)
...
This was bisected back to commit bfd40eaff5ab ("mm: fix
vma_is_anonymous() false-positives").
create_mspace_with_base() in the trace above, utilizes ashmem, and with
ashmem, for shared mappings we use shmem_zero_setup(), which sets the
vma->vm_ops to &shmem_vm_ops. But for private ashmem mappings nothing
sets the vma->vm_ops.
Looking at the problematic patch, it seems to add a requirement that one
call vma_set_anonymous() on a vma, otherwise the dummy_vm_ops will be
used. Using the dummy_vm_ops seem to triggger SIGBUS when traversing
unmapped pages.
Thus, this patch adds a call to vma_set_anonymous() for ashmem private
mappings and seems to avoid the reported problem.
Fixes: bfd40eaff5ab ("mm: fix vma_is_anonymous() false-positives")
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Colin Cross <ccross@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Reported-by: Amit Pundir <amit.pundir@linaro.org>
Reported-by: Youling 257 <youling257@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Christian Hoff