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Johannes Berg bfc58e2b98 um: remove process stub VMA 
This mostly reverts the old commit 3963333fe6 ("uml: cover stubs
with a VMA") which had added a VMA to the existing PTEs. However,
there's no real reason to have the PTEs in the first place and the
VMA cannot be 'fixed' in place, which leads to bugs that userspace
could try to unmap them and be forcefully killed, or such. Also,
there's a bit of an ugly hole in userspace's address space.

Simplify all this: just install the stub code/page at the top of
the (inner) address space, i.e. put it just above TASK_SIZE. The
pages are simply hard-coded to be mapped in the userspace process
we use to implement an mm context, and they're out of reach of the
inner mmap/munmap/mprotect etc. since they're above TASK_SIZE.

Getting rid of the VMA also makes vma_merge() no longer hit one of
the VM_WARN_ON()s there because we installed a VMA while the code
assumes the stack VMA is the first one.

It also removes a lockdep warning about mmap_sem usage since we no
longer have uml_setup_stubs() and thus no longer need to do any
manipulation that would require mmap_sem in activate_mm().

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
2021-02-12 21:37:38 +01:00
..
drivers um: Add SPDX headers for files in arch/um/os-Linux 2019-09-15 21:37:17 +02:00
skas um: remove process stub VMA 2021-02-12 21:37:38 +01:00
elf_aux.c
execvp.c
file.c um: Use fdatasync() when mapping the UBD FSYNC command 2020-06-02 22:37:55 +02:00
helper.c Revert "um: allocate a guard page to helper threads" 2021-01-26 22:11:38 +01:00
irq.c um: Monitor error events in IRQ controller 2020-12-13 22:38:28 +01:00
main.c um: Don't trace irqflags during shutdown 2019-11-25 22:42:57 +01:00
Makefile um: Increase stack frame size threshold for signal.c 2020-12-13 22:22:00 +01:00
mem.c um: Add SPDX headers for files in arch/um/os-Linux 2019-09-15 21:37:17 +02:00
process.c um: Add SPDX headers for files in arch/um/os-Linux 2019-09-15 21:37:17 +02:00
registers.c um: Add SPDX headers for files in arch/um/os-Linux 2019-09-15 21:37:17 +02:00
sigio.c um: irq/sigio: Support suspend/resume handling of workaround IRQs 2020-12-13 22:42:01 +01:00
signal.c um: time-travel: Correct time event IRQ delivery 2020-12-13 22:42:06 +01:00
start_up.c um: Add SPDX headers for files in arch/um/os-Linux 2019-09-15 21:37:17 +02:00
time.c um: fix os_idle_sleep() to not hang 2021-01-26 22:11:38 +01:00
tty.c um: Add SPDX headers for files in arch/um/os-Linux 2019-09-15 21:37:17 +02:00
umid.c um: Remove use of asprinf in umid.c 2020-12-13 22:21:07 +01:00
user_syms.c
util.c um: Some fixes to build UML with musl 2020-10-11 23:13:06 +02:00