On Thu, 19 Apr 2018, Michael S. Tsirkin wrote:
> Maybe make it conditional on CONFIG_DEBUG_SG too?
> Otherwise I think you just trigger a hard to debug memory corruption.
OK, here I resend the patch with CONFIG_DEBUG_SG. With CONFIG_DEBUG_SG,
the DMA API will print a stacktrace where the misuse happened, so it's
much easier to debug than with CONFIG_DEBUG_VM.
Fedora doesn't use CONFIG_DEBUG_SG in its default kernel (it only uses it
in the debugging kernel), so users won't be hurt by this.
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Subject: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG
The kvmalloc function tries to use kmalloc and falls back to vmalloc if
kmalloc fails.
Unfortunatelly, some kernel code has bugs - it uses kvmalloc and then
uses DMA-API on the returned memory or frees it with kfree. Such bugs were
found in the virtio-net driver, dm-integrity or RHEL7 powerpc-specific
code.
These bugs are hard to reproduce because vmalloc falls back to kmalloc
only if memory is fragmented.
In order to detect these bugs reliably I submit this patch that changes
kvmalloc to always use vmalloc if CONFIG_DEBUG_SG is turned on.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
---
mm/util.c | 2 ++
1 file changed, 2 insertions(+)
Index: linux-2.6/mm/util.c
===================================================================
--- linux-2.6.orig/mm/util.c 2018-04-18 15:46:23.000000000 +0200
+++ linux-2.6/mm/util.c 2018-04-19 23:14:14.000000000 +0200
@@ -395,6 +395,7 @@ EXPORT_SYMBOL(vm_mmap);
*/
void *kvmalloc_node(size_t size, gfp_t flags, int node)
{
+#ifndef CONFIG_DEBUG_SG
gfp_t kmalloc_flags = flags;
void *ret;
@@ -426,6 +427,7 @@ void *kvmalloc_node(size_t size, gfp_t f
*/
if (ret || size <= PAGE_SIZE)
return ret;
+#endif
return __vmalloc_node_flags_caller(size, node, flags,
__builtin_return_address(0));
