Messages in this thread Patch in this message | | | Date | Thu, 19 Apr 2018 17:27:06 -0400 (EDT) | From | Mikulas Patocka <> | Subject | [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG |
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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@redhat.com> 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@redhat.com>
--- 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));
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