The noexec support on s390 does not rely on a bit in the page table
entry but utilizes the secondary space mode to distinguish between
memory accesses for instructions vs. data. The noexec code relies
on the assumption that the cpu will always use the secondary space
page table for data accesses while it is running in the secondary
space mode. Up to the z9-109 class machines this has been the case.
Unfortunately this is not true anymore with z10 and later machines.
The load-relative-long instructions lrl, lgrl and lgfrl access the
memory operand using the same addressing-space mode that has been
used to fetch the instruction.
This breaks the noexec mode for all user space binaries compiled
with march=z10 or later. The only option is to remove the current
noexec support.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Introduce user_mode to replace the two variables switch_amode and
s390_noexec. There are three valid combinations of the old values:
1) switch_amode == 0 && s390_noexec == 0
2) switch_amode == 1 && s390_noexec == 0
3) switch_amode == 1 && s390_noexec == 1
They get replaced by
1) user_mode == HOME_SPACE_MODE
2) user_mode == PRIMARY_SPACE_MODE
3) user_mode == SECONDARY_SPACE_MODE
The new kernel parameter user_mode=[primary,secondary,home] lets
you choose the address space mode the user space processes should
use. In addition the CONFIG_S390_SWITCH_AMODE config option
is removed.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Suzuki Poulose reported the following recursive locking bug on s390:
Here is the stack trace : (see Appendix I for more info)
[<0000000000406ed6>] _spin_lock+0x52/0x94
[<0000000000103bde>] crst_table_free+0x14e/0x1a4
[<00000000001ba684>] __pmd_alloc+0x114/0x1ec
[<00000000001be8d0>] handle_mm_fault+0x2cc/0xb80
[<0000000000407d62>] do_dat_exception+0x2b6/0x3a0
[<0000000000114f8c>] sysc_return+0x0/0x8
[<00000200001642b2>] 0x200001642b2
The page_table_lock is already acquired in __pmd_alloc (mm/memory.c) and
it tries to populate the pud/pgd with a new pmd allocated. If another
thread populates it before we get a chance, we free the pmd using
pmd_free().
On s390x, pmd_free(even pud_free ) is #defined to crst_table_free(),
which acquires the page_table_lock to protect the crst_table index updates.
Hence this ends up in a recursive locking of the page_table_lock.
The solution suggested by Dave Hansen is to use a new spin lock in the mmu
context to protect the access to the crst_list and the pgtable_list.
Reported-by: Suzuki Poulose <suzuki@in.ibm.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Tell the compile that the clear_table inline assembly writes to the
memory referenced by *s.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
