On Tue, 10 Sep 2019 11:06:03 -0500 From: Mike Christie <mchristi@xxxxxxxxxx>
>
> > Really? Without any privilege check? So any random user can tap into
> > __GFP_NOIO allocations?
>
> That was a mistake on my part. I will add it in.
>
You may alternatively madvise a nutcracker as long as you would have
added a sledgehammer under /proc instead of a gavel.
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -45,6 +45,7 @@
#define MADV_SEQUENTIAL 2 /* expect sequential page references */
#define MADV_WILLNEED 3 /* will need these pages */
#define MADV_DONTNEED 4 /* don't need these pages */
+#define MADV_NOIO 5 /* set PF_MEMALLOC_NOIO */
/* common parameters: try to keep these consistent across architectures */
#define MADV_FREE 8 /* free pages only if memory pressure */
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -716,6 +716,7 @@ madvise_behavior_valid(int behavior)
case MADV_WILLNEED:
case MADV_DONTNEED:
case MADV_FREE:
+ case MADV_NOIO:
#ifdef CONFIG_KSM
case MADV_MERGEABLE:
case MADV_UNMERGEABLE:
@@ -813,6 +814,11 @@ SYSCALL_DEFINE3(madvise, unsigned long,
if (!madvise_behavior_valid(behavior))
return error;
+ if (behavior == MADV_NOIO) {
+ current->flags |= PF_MEMALLOC_NOIO;
+ return 0;
+ }
+
if (start & ~PAGE_MASK)
return error;
len = (len_in + ~PAGE_MASK) & PAGE_MASK;
