[PATCH v2 14/19] mm: Add vdso_base in mm_struct

Dmitry Safonov
2020-11-24T00:30:29Z

Instead of having every architecture to define vdso_base/vdso_addr etc,
provide a generic mechanism to track vdso_base for landing in userspace.
It'll minimize per-architecture difference, the number of callbacks to
provide.

Originally, it started from thread [1] where the need for .close()
callback on vm_special_mapping was pointed, this generic code besides
removing duplicated .mremap() callbacks provides a cheaper way to
support munmap() on vdso mappings without introducing .close() callbacks
for every architecture (with would bring even more code duplication).

[1]: https://lore.kernel.org/linux-arch/CAJwJo6ZANqYkSHbQ+3b+Fi_VT80MtrzEV5yreQAWx-L8j8x2zA@mail.gmail.com/
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 3 ++-
fs/aio.c | 3 ++-
include/linux/mm.h | 3 ++-
include/linux/mm_types.h | 10 ++++++++++
mm/Kconfig | 3 +++
mm/mmap.c | 19 ++++++++++++++++++-
mm/mremap.c | 2 +-
7 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index e916646adc69..786c97203bf6 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -1458,7 +1458,8 @@ static int pseudo_lock_dev_release(struct inode *inode, struct file *filp)
return 0;
}

-static int pseudo_lock_dev_mremap(struct vm_area_struct *area, unsigned long flags)
+static int pseudo_lock_dev_mremap(struct vm_area_struct *old_vma,
+ struct vm_area_struct *new_vma, unsigned long flags)
{
/* Not supported */
return -EINVAL;
diff --git a/fs/aio.c b/fs/aio.c
index d213be7b8a7e..9b205ebf17e8 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -323,7 +323,8 @@ static void aio_free_ring(struct kioctx *ctx)
}
}

-static int aio_ring_mremap(struct vm_area_struct *vma, unsigned long flags)
+static int aio_ring_mremap(struct vm_area_struct *old_vma,
+ struct vm_area_struct *vma, unsigned long flags)
{
struct file *file = vma->vm_file;
struct mm_struct *mm = vma->vm_mm;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a1c25da94663..dbda1b91f971 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -559,7 +559,8 @@ struct vm_operations_struct {
void (*close)(struct vm_area_struct * area);
/* Called any time before splitting to check if it's allowed */
int (*may_split)(struct vm_area_struct *area, unsigned long addr);
- int (*mremap)(struct vm_area_struct *area, unsigned long flags);
+ int (*mremap)(struct vm_area_struct *old_vma,
+ struct vm_area_struct *new_vma, unsigned long flags);
/*
* Called by mprotect() to make driver-specific permission
* checks before mprotect() is finalised. The VMA must not
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 95a257927dae..e1ca750874af 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -496,6 +496,16 @@ struct mm_struct {

/* Architecture-specific MM context */
mm_context_t context;
+#ifdef CONFIG_ARCH_HAS_VDSO_BASE
+ /*
+ * Address of special mapping VMA to land after processing
+ * a signal. Reads are unprotected: if a thread unmaps or
+ * mremaps the mapping while another thread is processing
+ * a signal, it can segfault while landing.
+ */
+ void __user *vdso_base;
+#endif
+#define UNMAPPED_VDSO_BASE TASK_SIZE_MAX

unsigned long flags; /* Must use atomic bitops to access */

diff --git a/mm/Kconfig b/mm/Kconfig
index 29904dc16bfc..941ae0597734 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -893,4 +893,7 @@ config SECRETMEM
select GENERIC_ALLOCATOR
select CMA

+config ARCH_HAS_VDSO_BASE
+ bool
+
endmenu
diff --git a/mm/mmap.c b/mm/mmap.c
index 17fe59a9780b..561afc3f1744 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -3409,11 +3409,25 @@ void vm_stat_account(struct mm_struct *mm, vm_flags_t flags, long npages)

static vm_fault_t special_mapping_fault(struct vm_fault *vmf);

+static void update_vdso_base(struct vm_area_struct *old_vma,
+ unsigned long new_addr)
+{
+#ifdef CONFIG_ARCH_HAS_VDSO_BASE
+ struct mm_struct *mm = old_vma->vm_mm;
+
+ if (WARN_ON_ONCE(!mm))
+ return;
+ if (old_vma->vm_start == (unsigned long)mm->vdso_base)
+ mm->vdso_base = (void __user *)new_addr;
+#endif
+}
+
/*
* Having a close hook prevents vma merging regardless of flags.
*/
static void special_mapping_close(struct vm_area_struct *vma)
{
+ update_vdso_base(vma, UNMAPPED_VDSO_BASE);
}

static const char *special_mapping_name(struct vm_area_struct *vma)
@@ -3421,7 +3435,8 @@ static const char *special_mapping_name(struct vm_area_struct *vma)
return ((struct vm_special_mapping *)vma->vm_private_data)->name;
}

-static int special_mapping_mremap(struct vm_area_struct *new_vma,
+static int special_mapping_mremap(struct vm_area_struct *old_vma,
+ struct vm_area_struct *new_vma,
unsigned long flags)
{
struct vm_special_mapping *sm = new_vma->vm_private_data;
@@ -3435,6 +3450,8 @@ static int special_mapping_mremap(struct vm_area_struct *new_vma,
if (sm->mremap)
sm->mremap(sm, new_vma);

+ update_vdso_base(old_vma, new_vma->vm_start);
+
return 0;
}

diff --git a/mm/mremap.c b/mm/mremap.c
index c5590afe7165..9595f6b72101 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -543,7 +543,7 @@ static unsigned long move_vma(struct vm_area_struct *vma,
if (moved_len < old_len) {
err = -ENOMEM;
} else if (vma->vm_ops && vma->vm_ops->mremap) {
- err = vma->vm_ops->mremap(new_vma, flags);
+ err = vma->vm_ops->mremap(vma, new_vma, flags);
}

if (unlikely(err)) {
--
2.29.2