[PATCH AUTOSEL 4.19 056/191] s390/vdso: avoid 64-bit vdso mapping for compat tasks

Sasha Levin
2019-11-10T02:42:15Z

From: Vasily Gorbik <gor@linux.ibm.com>

[ Upstream commit d1befa65823e9c6d013883b8a41d081ec338c489 ]

vdso_fault used is_compat_task function (on s390 it tests "current"
thread_info flags) to distinguish compat tasks and map 31-bit vdso
pages. But "current" task might not correspond to mm context.

When 31-bit compat inferior is executed under gdb, gdb does
PTRACE_PEEKTEXT on vdso page, causing vdso_fault with "current" being
64-bit gdb process. So, 31-bit inferior ends up with 64-bit vdso mapped.

To avoid this problem a new compat_mm flag has been introduced into
mm context. This flag is used in vdso_fault and vdso_mremap instead
of is_compat_task.

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/s390/include/asm/mmu.h | 2 ++
arch/s390/include/asm/mmu_context.h | 1 +
arch/s390/kernel/vdso.c | 8 +++++---
3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/mmu.h b/arch/s390/include/asm/mmu.h
index a8418e1379eb7..bcfb6371086f2 100644
--- a/arch/s390/include/asm/mmu.h
+++ b/arch/s390/include/asm/mmu.h
@@ -32,6 +32,8 @@ typedef struct {
unsigned int uses_cmm:1;
/* The gmaps associated with this context are allowed to use huge pages. */
unsigned int allow_gmap_hpage_1m:1;
+ /* The mmu context is for compat task */
+ unsigned int compat_mm:1;
} mm_context_t;

#define INIT_MM_CONTEXT(name) \
diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
index 09b61d0e491f6..e4462202200d7 100644
--- a/arch/s390/include/asm/mmu_context.h
+++ b/arch/s390/include/asm/mmu_context.h
@@ -25,6 +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;
#ifdef CONFIG_PGSTE
mm->context.alloc_pgste = page_table_allocate_pgste ||
test_thread_flag(TIF_PGSTE) ||
diff --git a/arch/s390/kernel/vdso.c b/arch/s390/kernel/vdso.c
index 3031cc6dd0ab4..ec31b48a42a52 100644
--- a/arch/s390/kernel/vdso.c
+++ b/arch/s390/kernel/vdso.c
@@ -56,7 +56,7 @@ static vm_fault_t vdso_fault(const struct vm_special_mapping *sm,
vdso_pagelist = vdso64_pagelist;
vdso_pages = vdso64_pages;
#ifdef CONFIG_COMPAT
- if (is_compat_task()) {
+ if (vma->vm_mm->context.compat_mm) {
vdso_pagelist = vdso32_pagelist;
vdso_pages = vdso32_pages;
}
@@ -77,7 +77,7 @@ static int vdso_mremap(const struct vm_special_mapping *sm,

vdso_pages = vdso64_pages;
#ifdef CONFIG_COMPAT
- if (is_compat_task())
+ if (vma->vm_mm->context.compat_mm)
vdso_pages = vdso32_pages;
#endif

@@ -224,8 +224,10 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)

vdso_pages = vdso64_pages;
#ifdef CONFIG_COMPAT
- if (is_compat_task())
+ if (is_compat_task()) {
vdso_pages = vdso32_pages;
+ mm->context.compat_mm = 1;
+ }
#endif
/*
* vDSO has a problem and was disabled, just don't "enable" it for
--
2.20.1