# git rev-parse -q --verify 8c1684bb81f173543599f1848c29a2a3b1ee5907^{commit}
8c1684bb81f173543599f1848c29a2a3b1ee5907
already have revision, skipping fetch
# git checkout -q -f -B kisskb 8c1684bb81f173543599f1848c29a2a3b1ee5907
# git clean -qxdf
# < git log -1
# commit 8c1684bb81f173543599f1848c29a2a3b1ee5907
# Merge: f44d5c489051 3f2c788a1314
# Author: Linus Torvalds <torvalds@linux-foundation.org>
# Date:   Thu May 14 11:52:28 2020 -0700
# 
#     Merge tag 'for-linus-2020-05-13' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux
#     
#     Pull thread fix from Christian Brauner:
#      "This contains a single fix for all exported legacy fork helpers to
#       block accidental access to clone3() features in the upper 32 bits of
#       their respective flags arguments.
#     
#       I got Cced on a glibc issue where someone reported consistent failures
#       for the legacy clone() syscall on ppc64le when sign extension was
#       performed (since the clone() syscall in glibc exposes the flags
#       argument as an int whereas the kernel uses unsigned long).
#     
#       The legacy clone() syscall is odd in a bunch of ways and here two
#       things interact:
#     
#        - First, legacy clone's flag argument is word-size dependent, i.e.
#          it's an unsigned long whereas most system calls with flag arguments
#          use int or unsigned int.
#     
#        - Second, legacy clone() ignores unknown and deprecated flags.
#     
#       The two of them taken together means that users on 64bit systems can
#       pass garbage for the upper 32bit of the clone() syscall since forever
#       and things would just work fine.
#     
#       The following program compiled on a 64bit kernel prior to v5.7-rc1
#       will succeed and will fail post v5.7-rc1 with EBADF:
#     
#         int main(int argc, char *argv[])
#         {
#               pid_t pid;
#     
#               /* Note that legacy clone() has different argument ordering on
#                * different architectures so this won't work everywhere.
#                *
#                * Only set the upper 32 bits.
#                */
#               pid = syscall(__NR_clone, 0xffffffff00000000 | SIGCHLD,
#                             NULL, NULL, NULL, NULL);
#               if (pid < 0)
#                       exit(EXIT_FAILURE);
#               if (pid == 0)
#                       exit(EXIT_SUCCESS);
#               if (wait(NULL) != pid)
#                       exit(EXIT_FAILURE);
#     
#               exit(EXIT_SUCCESS);
#         }
#     
#       Since legacy clone() couldn't be extended this was not a problem so
#       far and nobody really noticed or cared since nothing in the kernel
#       ever bothered to look at the upper 32 bits.
#     
#       But once we introduced clone3() and expanded the flag argument in
#       struct clone_args to 64 bit we opened this can of worms. With the
#       first flag-based extension to clone3() making use of the upper 32 bits
#       of the flag argument we've effectively made it possible for the legacy
#       clone() syscall to reach clone3() only flags on accident. The sign
#       extension scenario is just the odd corner-case that we needed to
#       figure this out.
#     
#       The reason we just realized this now and not already when we
#       introduced CLONE_CLEAR_SIGHAND was that CLONE_INTO_CGROUP assumes that
#       a valid cgroup file descriptor has been given - whereas
#       CLONE_CLEAR_SIGHAND doesn't need to verify anything. It just silently
#       resets the signal handlers to SIG_DFL.
#     
#       So the sign extension (or the user accidently passing garbage for the
#       upper 32 bits) caused the CLONE_INTO_CGROUP bit to be raised and the
#       kernel to error out when it didn't find a valid cgroup file
#       descriptor.
#     
#       Note, I'm also capping kernel_thread()'s flag argument mainly because
#       none of the new features make sense for kernel_thread() and we
#       shouldn't risk them being accidently activated however unlikely. If we
#       wanted to, we could even make kernel_thread() yell when an unknown
#       flag has been set which it doesn't do right now. But it's not worth
#       risking this in a bugfix imho"
#     
#     * tag 'for-linus-2020-05-13' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux:
#       fork: prevent accidental access to clone3 features
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-gcc --version
# < /opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-ld --version
# < git log --format=%s --max-count=1 8c1684bb81f173543599f1848c29a2a3b1ee5907
# < make -s -j 80 ARCH=arm O=/kisskb/build/linus_u8500_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  u8500_defconfig
# < make -s -j 80 ARCH=arm O=/kisskb/build/linus_u8500_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  help
# make -s -j 80 ARCH=arm O=/kisskb/build/linus_u8500_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  olddefconfig
# make -s -j 80 ARCH=arm O=/kisskb/build/linus_u8500_defconfig_arm-gcc4.9 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-4.9.4-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-  
/kisskb/src/drivers/gpu/drm/drm_dp_mst_topology.c: In function 'drm_dp_mst_dsc_aux_for_port':
/kisskb/src/drivers/gpu/drm/drm_dp_mst_topology.c:5502:9: warning: missing braces around initializer [-Wmissing-braces]
  struct drm_dp_desc desc = { 0 };
         ^
/kisskb/src/drivers/gpu/drm/drm_dp_mst_topology.c:5502:9: warning: (near initialization for 'desc.ident') [-Wmissing-braces]
Completed OK
# rm -rf /kisskb/build/linus_u8500_defconfig_arm-gcc4.9
# Build took: 0:01:29.426132