Commit 190f056f authored Jan 02, 2019 by Vasily Gorbik Committed by Martin Schwidefsky Jan 11, 2019

s390/vdso: correct vdso mapping for compat tasks



While "s390/vdso: avoid 64-bit vdso mapping for compat tasks" fixed
64-bit vdso mapping for compat tasks under gdb it introduced another
problem. "compat_mm" flag is not inherited during fork and when
31-bit process forks a child (but does not perform exec) it ends up
with 64-bit vdso. To address that, init_new_context (which is called
during fork and exec) now initialize compat_mm based on thread TIF_31BIT
flag. Later compat_mm is adjusted in arch_setup_additional_pages, which
is called during exec.

Fixes: d1befa65 ("s390/vdso: avoid 64-bit vdso mapping for compat tasks")
Reported-by: Stefan Liebler <stli@linux.ibm.com>
Reviewed-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: <stable@vger.kernel.org> # v4.20+
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

parent b7cb707c

arch/s390/include/asm/mmu_context.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -25,7 +25,7 @@ static inline int init_new_context(struct task_struct *tsk,
		atomic_set(&mm->context.flush_count, 0);
		mm->context.gmap_asce = 0;
		mm->context.flush_mm = 0;
		mm->context.compat_mm = 0;
		mm->context.compat_mm = test_thread_flag(TIF_31BIT);
		#ifdef CONFIG_PGSTE
		mm->context.alloc_pgste = page_table_allocate_pgste \|\|
		test_thread_flag(TIF_PGSTE) \|\|

arch/s390/kernel/vdso.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -224,10 +224,9 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)

		vdso_pages = vdso64_pages;
		#ifdef CONFIG_COMPAT
		if (is_compat_task()) {
		mm->context.compat_mm = is_compat_task();
		if (mm->context.compat_mm)
		vdso_pages = vdso32_pages;
		mm->context.compat_mm = 1;
		}
		#endif
		/*
		* vDSO has a problem and was disabled, just don't "enable" it for

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