s390/vdso: avoid 64-bit vdso mapping for compat tasks

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>

diff --git a/arch/s390/include/asm/mmu.h b/arch/s390/include/asm/mmu.h
index a8418e1..bcfb637 100644 (file)
--- 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 0717ee7..dbd689d 100644 (file)
--- 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 3031cc6..ec31b48 100644 (file)
--- 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