On Mon, Mar 18, 2019 at 12:47 PM Kevin Brodsky [off-list ref] wrote:

On 15/03/2019 19:51, Andrey Konovalov wrote:

quoted

This patch is a part of a series that extends arm64 kernel ABI to allow to
pass tagged user pointers (with the top byte set to something else other
than 0x00) as syscall arguments.

prctl_set_mm() and prctl_set_mm_map() use provided user pointers for vma
lookups, which can only by done with untagged pointers.

Untag user pointers in these functions.

Signed-off-by: Andrey Konovalov <redacted>
---
  kernel/sys.c | 14 ++++++++++++++
  1 file changed, 14 insertions(+)

diff --git a/kernel/sys.c b/kernel/sys.c
index 12df0e5434b8..8e56d87cc6db 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c

@@ -1993,6 +1993,18 @@ static int prctl_set_mm_map(int opt, const void __user *addr, unsigned long data
      if (copy_from_user(&prctl_map, addr, sizeof(prctl_map)))
              return -EFAULT;

+     prctl_map->start_code   = untagged_addr(prctl_map.start_code);
+     prctl_map->end_code     = untagged_addr(prctl_map.end_code);
+     prctl_map->start_data   = untagged_addr(prctl_map.start_data);
+     prctl_map->end_data     = untagged_addr(prctl_map.end_data);
+     prctl_map->start_brk    = untagged_addr(prctl_map.start_brk);
+     prctl_map->brk          = untagged_addr(prctl_map.brk);
+     prctl_map->start_stack  = untagged_addr(prctl_map.start_stack);
+     prctl_map->arg_start    = untagged_addr(prctl_map.arg_start);
+     prctl_map->arg_end      = untagged_addr(prctl_map.arg_end);
+     prctl_map->env_start    = untagged_addr(prctl_map.env_start);
+     prctl_map->env_end      = untagged_addr(prctl_map.env_end);

As the buildbot suggests, those -> should be . instead :) You might want to check
your local build with CONFIG_CHECKPOINT_RESTORE=y.

Oops :)

quoted

+
      error = validate_prctl_map(&prctl_map);
      if (error)
              return error;

@@ -2106,6 +2118,8 @@ static int prctl_set_mm(int opt, unsigned long addr,
                            opt != PR_SET_MM_MAP_SIZE)))
              return -EINVAL;

+     addr = untagged_addr(addr);

This is a bit too coarse, addr is indeed used for find_vma() later on, but it is also
used to access memory, by prctl_set_mm_mmap() and prctl_set_auxv().

Yes, I wrote this patch before our Friday discussion and forgot about
it. I'll fix it in v12, thanks!

Kevin

quoted

+
  #ifdef CONFIG_CHECKPOINT_RESTORE
      if (opt == PR_SET_MM_MAP || opt == PR_SET_MM_MAP_SIZE)
              return prctl_set_mm_map(opt, (const void __user *)addr, arg4);