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SubjectRe: [PATCH v5] fault-injection: introduce kvmalloc fallback options
On Wed, 25 Apr 2018, Mikulas Patocka wrote:

> From: Mikulas Patocka <mpatocka@redhat.com>
> Subject: [PATCH] fault-injection: introduce kvmalloc fallback options
>
> This patch introduces a fault-injection option "kvmalloc_fallback". This
> option makes kvmalloc randomly fall back to vmalloc.
>
> Unfortunately, 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. This options helps to test for these bugs.
>
> The patch introduces a config option FAIL_KVMALLOC_FALLBACK_PROBABILITY.
> It can be enabled in distribution debug kernels, so that kvmalloc abuse
> can be tested by the users. The default can be overridden with
> "kvmalloc_fallback" parameter or in /sys/kernel/debug/kvmalloc_fallback/.
>

Do we really need the new config option? This could just be manually
tunable via fault injection IIUC.

> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
>
> ---
> Documentation/fault-injection/fault-injection.txt | 7 +++++
> include/linux/fault-inject.h | 9 +++---
> kernel/futex.c | 2 -
> lib/Kconfig.debug | 15 +++++++++++
> mm/failslab.c | 2 -
> mm/page_alloc.c | 2 -
> mm/util.c | 30 ++++++++++++++++++++++
> 7 files changed, 60 insertions(+), 7 deletions(-)
>
> Index: linux-2.6/Documentation/fault-injection/fault-injection.txt
> ===================================================================
> --- linux-2.6.orig/Documentation/fault-injection/fault-injection.txt 2018-04-16 21:08:34.000000000 +0200
> +++ linux-2.6/Documentation/fault-injection/fault-injection.txt 2018-04-25 21:36:36.000000000 +0200
> @@ -15,6 +15,12 @@ o fail_page_alloc
>
> injects page allocation failures. (alloc_pages(), get_free_pages(), ...)
>
> +o kvmalloc_fallback
> +
> + makes the function kvmalloc randomly fall back to vmalloc. This could be used
> + to detects bugs such as using DMA-API on the result of kvmalloc or freeing
> + the result of kvmalloc with free.
> +
> o fail_futex
>
> injects futex deadlock and uaddr fault errors.
> @@ -167,6 +173,7 @@ use the boot option:
>
> failslab=
> fail_page_alloc=
> + kvmalloc_fallback=
> fail_make_request=
> fail_futex=
> mmc_core.fail_request=<interval>,<probability>,<space>,<times>
> Index: linux-2.6/include/linux/fault-inject.h
> ===================================================================
> --- linux-2.6.orig/include/linux/fault-inject.h 2018-04-16 21:08:36.000000000 +0200
> +++ linux-2.6/include/linux/fault-inject.h 2018-04-25 21:38:22.000000000 +0200
> @@ -31,17 +31,18 @@ struct fault_attr {
> struct dentry *dname;
> };
>
> -#define FAULT_ATTR_INITIALIZER { \
> +#define FAULT_ATTR_INITIALIZER(p) { \
> + .probability = (p), \
> .interval = 1, \
> - .times = ATOMIC_INIT(1), \
> + .times = ATOMIC_INIT((p) ? -1 : 1), \
> + .verbose = (p) ? 0 : 2, \
> .require_end = ULONG_MAX, \
> .stacktrace_depth = 32, \
> .ratelimit_state = RATELIMIT_STATE_INIT_DISABLED, \
> - .verbose = 2, \
> .dname = NULL, \
> }
>
> -#define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER
> +#define DECLARE_FAULT_ATTR(name) struct fault_attr name = FAULT_ATTR_INITIALIZER(0)
> int setup_fault_attr(struct fault_attr *attr, char *str);
> bool should_fail(struct fault_attr *attr, ssize_t size);
>
> Index: linux-2.6/lib/Kconfig.debug
> ===================================================================
> --- linux-2.6.orig/lib/Kconfig.debug 2018-04-25 15:56:16.000000000 +0200
> +++ linux-2.6/lib/Kconfig.debug 2018-04-25 21:39:45.000000000 +0200
> @@ -1527,6 +1527,21 @@ config FAIL_PAGE_ALLOC
> help
> Provide fault-injection capability for alloc_pages().
>
> +config FAIL_KVMALLOC_FALLBACK_PROBABILITY
> + int "Default kvmalloc fallback probability"
> + depends on FAULT_INJECTION
> + range 0 100
> + default "0"
> + help
> + This option will make kvmalloc randomly fall back to vmalloc.
> + Normally, kvmalloc falls back to vmalloc only rarely, if memory
> + is fragmented.
> +
> + This option helps to detect hard-to-reproduce driver bugs, for
> + example using DMA API on the result of kvmalloc.
> +
> + The default may be overridden with the kvmalloc_fallback parameter.
> +
> config FAIL_MAKE_REQUEST
> bool "Fault-injection capability for disk IO"
> depends on FAULT_INJECTION && BLOCK
> Index: linux-2.6/mm/util.c
> ===================================================================
> --- linux-2.6.orig/mm/util.c 2018-04-25 15:48:39.000000000 +0200
> +++ linux-2.6/mm/util.c 2018-04-25 21:43:31.000000000 +0200
> @@ -14,6 +14,7 @@
> #include <linux/hugetlb.h>
> #include <linux/vmalloc.h>
> #include <linux/userfaultfd_k.h>
> +#include <linux/fault-inject.h>
>
> #include <asm/sections.h>
> #include <linux/uaccess.h>
> @@ -377,6 +378,29 @@ unsigned long vm_mmap(struct file *file,
> }
> EXPORT_SYMBOL(vm_mmap);
>
> +#ifdef CONFIG_FAULT_INJECTION
> +
> +static struct fault_attr kvmalloc_fallback =
> + FAULT_ATTR_INITIALIZER(CONFIG_FAIL_KVMALLOC_FALLBACK_PROBABILITY);
> +
> +static int __init setup_kvmalloc_fallback(char *str)
> +{
> + return setup_fault_attr(&kvmalloc_fallback, str);
> +}
> +
> +__setup("kvmalloc_fallback=", setup_kvmalloc_fallback);
> +
> +#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
> +static int __init kvmalloc_fallback_debugfs_init(void)
> +{
> + fault_create_debugfs_attr("kvmalloc_fallback", NULL, &kvmalloc_fallback);
> + return 0;
> +}
> +late_initcall(kvmalloc_fallback_debugfs_init);
> +#endif
> +
> +#endif
> +
> /**
> * kvmalloc_node - attempt to allocate physically contiguous memory, but upon
> * failure, fall back to non-contiguous (vmalloc) allocation.
> @@ -404,6 +428,11 @@ void *kvmalloc_node(size_t size, gfp_t f
> */
> WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL);
>
> +#ifdef CONFIG_FAULT_INJECTION
> + if (should_fail(&kvmalloc_fallback, size))
> + goto do_vmalloc;
> +#endif
> +
> /*
> * We want to attempt a large physically contiguous block first because
> * it is less likely to fragment multiple larger blocks and therefore
> @@ -427,6 +456,7 @@ void *kvmalloc_node(size_t size, gfp_t f
> if (ret || size <= PAGE_SIZE)
> return ret;
>
> +do_vmalloc: __maybe_unused
> return __vmalloc_node_flags_caller(size, node, flags,
> __builtin_return_address(0));
> }
> Index: linux-2.6/kernel/futex.c
> ===================================================================
> --- linux-2.6.orig/kernel/futex.c 2018-02-14 20:24:42.000000000 +0100
> +++ linux-2.6/kernel/futex.c 2018-04-25 21:11:33.000000000 +0200
> @@ -288,7 +288,7 @@ static struct {
>
> bool ignore_private;
> } fail_futex = {
> - .attr = FAULT_ATTR_INITIALIZER,
> + .attr = FAULT_ATTR_INITIALIZER(0),
> .ignore_private = false,
> };
>
> Index: linux-2.6/mm/failslab.c
> ===================================================================
> --- linux-2.6.orig/mm/failslab.c 2018-04-16 21:08:36.000000000 +0200
> +++ linux-2.6/mm/failslab.c 2018-04-25 21:11:40.000000000 +0200
> @@ -9,7 +9,7 @@ static struct {
> bool ignore_gfp_reclaim;
> bool cache_filter;
> } failslab = {
> - .attr = FAULT_ATTR_INITIALIZER,
> + .attr = FAULT_ATTR_INITIALIZER(0),
> .ignore_gfp_reclaim = true,
> .cache_filter = false,
> };
> Index: linux-2.6/mm/page_alloc.c
> ===================================================================
> --- linux-2.6.orig/mm/page_alloc.c 2018-04-16 21:08:36.000000000 +0200
> +++ linux-2.6/mm/page_alloc.c 2018-04-25 21:11:47.000000000 +0200
> @@ -3055,7 +3055,7 @@ static struct {
> bool ignore_gfp_reclaim;
> u32 min_order;
> } fail_page_alloc = {
> - .attr = FAULT_ATTR_INITIALIZER,
> + .attr = FAULT_ATTR_INITIALIZER(0),
> .ignore_gfp_reclaim = true,
> .ignore_gfp_highmem = true,
> .min_order = 1,
>
>

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