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Message-ID: <CAG_fn=XvG5atw4qEOKRB0ZmBf5uMutFEV1zVVv6fUTtV_2+bBw@mail.gmail.com>
Date: Tue, 31 May 2022 13:08:25 +0200
From: Alexander Potapenko <glider@...gle.com>
To: Marco Elver <elver@...gle.com>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrey Konovalov <andreyknvl@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
Christoph Hellwig <hch@....de>,
Christoph Lameter <cl@...ux.com>,
David Rientjes <rientjes@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Herbert Xu <herbert@...dor.apana.org.au>,
Ilya Leoshkevich <iii@...ux.ibm.com>,
Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Kees Cook <keescook@...omium.org>,
Mark Rutland <mark.rutland@....com>,
Matthew Wilcox <willy@...radead.org>,
"Michael S. Tsirkin" <mst@...hat.com>,
Pekka Enberg <penberg@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Petr Mladek <pmladek@...e.com>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>,
Vasily Gorbik <gor@...ux.ibm.com>,
Vegard Nossum <vegard.nossum@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>,
kasan-dev <kasan-dev@...glegroups.com>,
Linux Memory Management List <linux-mm@...ck.org>,
Linux-Arch <linux-arch@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 12/46] kmsan: add KMSAN runtime core
On Wed, Apr 27, 2022 at 4:10 PM Marco Elver <elver@...gle.com> wrote:
>
> On Tue, Apr 26, 2022 at 06:42PM +0200, Alexander Potapenko wrote:
> > For each memory location KernelMemorySanitizer maintains two types of
> > metadata:
> > 1. The so-called shadow of that location - а byte:byte mapping describing
> > whether or not individual bits of memory are initialized (shadow is 0)
> > or not (shadow is 1).
> > 2. The origins of that location - а 4-byte:4-byte mapping containing
> > 4-byte IDs of the stack traces where uninitialized values were
> > created.
> >
> > Each struct page now contains pointers to two struct pages holding
> > KMSAN metadata (shadow and origins) for the original struct page.
> > Utility routines in mm/kmsan/core.c and mm/kmsan/shadow.c handle the
> > metadata creation, addressing, copying and checking.
> > mm/kmsan/report.c performs error reporting in the cases an uninitialized
> > value is used in a way that leads to undefined behavior.
> >
> > KMSAN compiler instrumentation is responsible for tracking the metadata
> > along with the kernel memory. mm/kmsan/instrumentation.c provides the
> > implementation for instrumentation hooks that are called from files
> > compiled with -fsanitize=kernel-memory.
> >
> > To aid parameter passing (also done at instrumentation level), each
> > task_struct now contains a struct kmsan_task_state used to track the
> > metadata of function parameters and return values for that task.
> >
> > Finally, this patch provides CONFIG_KMSAN that enables KMSAN, and
> > declares CFLAGS_KMSAN, which are applied to files compiled with KMSAN.
> > The KMSAN_SANITIZE:=n Makefile directive can be used to completely
> > disable KMSAN instrumentation for certain files.
> >
> > Similarly, KMSAN_ENABLE_CHECKS:=n disables KMSAN checks and makes newly
> > created stack memory initialized.
> >
> > Users can also use functions from include/linux/kmsan-checks.h to mark
> > certain memory regions as uninitialized or initialized (this is called
> > "poisoning" and "unpoisoning") or check that a particular region is
> > initialized.
> >
> > Signed-off-by: Alexander Potapenko <glider@...gle.com>
> > ---
> > v2:
> > -- as requested by Greg K-H, moved hooks for different subsystems to respective patches,
> > rewrote the patch description;
> > -- addressed comments by Dmitry Vyukov;
> > -- added a note about KMSAN being not intended for production use.
> > -- fix case of unaligned dst in kmsan_internal_memmove_metadata()
> >
> > v3:
> > -- print build IDs in reports where applicable
> > -- drop redundant filter_irq_stacks(), unpoison the local passed to __stack_depot_save()
> > -- remove a stray BUG()
> >
> > Link: https://linux-review.googlesource.com/id/I9b71bfe3425466c97159f9de0062e5e8e4fec866
> > ---
> > Makefile | 1 +
> > include/linux/kmsan-checks.h | 64 +++++
> > include/linux/kmsan.h | 47 ++++
> > include/linux/mm_types.h | 12 +
> > include/linux/sched.h | 5 +
> > lib/Kconfig.debug | 1 +
> > lib/Kconfig.kmsan | 23 ++
> > mm/Makefile | 1 +
> > mm/kmsan/Makefile | 18 ++
> > mm/kmsan/core.c | 458 +++++++++++++++++++++++++++++++++++
> > mm/kmsan/hooks.c | 66 +++++
> > mm/kmsan/instrumentation.c | 267 ++++++++++++++++++++
> > mm/kmsan/kmsan.h | 183 ++++++++++++++
> > mm/kmsan/report.c | 211 ++++++++++++++++
> > mm/kmsan/shadow.c | 186 ++++++++++++++
> > scripts/Makefile.kmsan | 1 +
> > scripts/Makefile.lib | 9 +
> > 17 files changed, 1553 insertions(+)
> > create mode 100644 include/linux/kmsan-checks.h
> > create mode 100644 include/linux/kmsan.h
> > create mode 100644 lib/Kconfig.kmsan
> > create mode 100644 mm/kmsan/Makefile
> > create mode 100644 mm/kmsan/core.c
> > create mode 100644 mm/kmsan/hooks.c
> > create mode 100644 mm/kmsan/instrumentation.c
> > create mode 100644 mm/kmsan/kmsan.h
> > create mode 100644 mm/kmsan/report.c
> > create mode 100644 mm/kmsan/shadow.c
> > create mode 100644 scripts/Makefile.kmsan
> >
> > diff --git a/Makefile b/Makefile
> > index c3ec1ea423797..d3c7dcd9f0fea 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1009,6 +1009,7 @@ include-y := scripts/Makefile.extrawarn
> > include-$(CONFIG_DEBUG_INFO) += scripts/Makefile.debug
> > include-$(CONFIG_KASAN) += scripts/Makefile.kasan
> > include-$(CONFIG_KCSAN) += scripts/Makefile.kcsan
> > +include-$(CONFIG_KMSAN) += scripts/Makefile.kmsan
> > include-$(CONFIG_UBSAN) += scripts/Makefile.ubsan
> > include-$(CONFIG_KCOV) += scripts/Makefile.kcov
> > include-$(CONFIG_GCC_PLUGINS) += scripts/Makefile.gcc-plugins
> > diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h
> > new file mode 100644
> > index 0000000000000..a6522a0c28df9
> > --- /dev/null
> > +++ b/include/linux/kmsan-checks.h
> > @@ -0,0 +1,64 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * KMSAN checks to be used for one-off annotations in subsystems.
> > + *
> > + * Copyright (C) 2017-2022 Google LLC
> > + * Author: Alexander Potapenko <glider@...gle.com>
> > + *
> > + */
> > +
> > +#ifndef _LINUX_KMSAN_CHECKS_H
> > +#define _LINUX_KMSAN_CHECKS_H
> > +
> > +#include <linux/types.h>
> > +
> > +#ifdef CONFIG_KMSAN
> > +
> > +/**
> > + * kmsan_poison_memory() - Mark the memory range as uninitialized.
> > + * @address: address to start with.
> > + * @size: size of buffer to poison.
> > + * @flags: GFP flags for allocations done by this function.
> > + *
> > + * Until other data is written to this range, KMSAN will treat it as
> > + * uninitialized. Error reports for this memory will reference the call site of
> > + * kmsan_poison_memory() as origin.
> > + */
> > +void kmsan_poison_memory(const void *address, size_t size, gfp_t flags);
> > +
> > +/**
> > + * kmsan_unpoison_memory() - Mark the memory range as initialized.
> > + * @address: address to start with.
> > + * @size: size of buffer to unpoison.
> > + *
> > + * Until other data is written to this range, KMSAN will treat it as
> > + * initialized.
> > + */
> > +void kmsan_unpoison_memory(const void *address, size_t size);
> > +
> > +/**
> > + * kmsan_check_memory() - Check the memory range for being initialized.
> > + * @address: address to start with.
> > + * @size: size of buffer to check.
> > + *
> > + * If any piece of the given range is marked as uninitialized, KMSAN will report
> > + * an error.
> > + */
> > +void kmsan_check_memory(const void *address, size_t size);
> > +
> > +#else
> > +
> > +static inline void kmsan_poison_memory(const void *address, size_t size,
> > + gfp_t flags)
> > +{
> > +}
> > +static inline void kmsan_unpoison_memory(const void *address, size_t size)
> > +{
> > +}
> > +static inline void kmsan_check_memory(const void *address, size_t size)
> > +{
> > +}
> > +
> > +#endif
> > +
> > +#endif /* _LINUX_KMSAN_CHECKS_H */
> > diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
> > new file mode 100644
> > index 0000000000000..4e35f43eceaa9
> > --- /dev/null
> > +++ b/include/linux/kmsan.h
> > @@ -0,0 +1,47 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * KMSAN API for subsystems.
> > + *
> > + * Copyright (C) 2017-2022 Google LLC
> > + * Author: Alexander Potapenko <glider@...gle.com>
> > + *
> > + */
> > +#ifndef _LINUX_KMSAN_H
> > +#define _LINUX_KMSAN_H
> > +
> > +#include <linux/gfp.h>
> > +#include <linux/kmsan-checks.h>
> > +#include <linux/stackdepot.h>
> > +#include <linux/types.h>
> > +#include <linux/vmalloc.h>
> > +
> > +struct page;
> > +
> > +#ifdef CONFIG_KMSAN
> > +
> > +/* These constants are defined in the MSan LLVM instrumentation pass. */
> > +#define KMSAN_RETVAL_SIZE 800
> > +#define KMSAN_PARAM_SIZE 800
> > +
> > +struct kmsan_context_state {
> > + char param_tls[KMSAN_PARAM_SIZE];
> > + char retval_tls[KMSAN_RETVAL_SIZE];
> > + char va_arg_tls[KMSAN_PARAM_SIZE];
> > + char va_arg_origin_tls[KMSAN_PARAM_SIZE];
> > + u64 va_arg_overflow_size_tls;
> > + char param_origin_tls[KMSAN_PARAM_SIZE];
> > + depot_stack_handle_t retval_origin_tls;
> > +};
> > +
> > +#undef KMSAN_PARAM_SIZE
> > +#undef KMSAN_RETVAL_SIZE
> > +
> > +struct kmsan_ctx {
> > + struct kmsan_context_state cstate;
> > + int kmsan_in_runtime;
> > + bool allow_reporting;
> > +};
> > +
> > +#endif
> > +
> > +#endif /* _LINUX_KMSAN_H */
> > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > index 8834e38c06a4f..85c97a2145f7e 100644
> > --- a/include/linux/mm_types.h
> > +++ b/include/linux/mm_types.h
> > @@ -218,6 +218,18 @@ struct page {
> > not kmapped, ie. highmem) */
> > #endif /* WANT_PAGE_VIRTUAL */
> >
> > +#ifdef CONFIG_KMSAN
> > + /*
> > + * KMSAN metadata for this page:
> > + * - shadow page: every bit indicates whether the corresponding
> > + * bit of the original page is initialized (0) or not (1);
> > + * - origin page: every 4 bytes contain an id of the stack trace
> > + * where the uninitialized value was created.
> > + */
> > + struct page *kmsan_shadow;
> > + struct page *kmsan_origin;
> > +#endif
> > +
> > #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
> > int _last_cpupid;
> > #endif
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index a8911b1f35aad..9e53624cd73ac 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -14,6 +14,7 @@
> > #include <linux/pid.h>
> > #include <linux/sem.h>
> > #include <linux/shm.h>
> > +#include <linux/kmsan.h>
> > #include <linux/mutex.h>
> > #include <linux/plist.h>
> > #include <linux/hrtimer.h>
> > @@ -1352,6 +1353,10 @@ struct task_struct {
> > #endif
> > #endif
> >
> > +#ifdef CONFIG_KMSAN
> > + struct kmsan_ctx kmsan_ctx;
> > +#endif
> > +
> > #if IS_ENABLED(CONFIG_KUNIT)
> > struct kunit *kunit_test;
> > #endif
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 075cd25363ac3..b81670878acae 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -996,6 +996,7 @@ config DEBUG_STACKOVERFLOW
> >
> > source "lib/Kconfig.kasan"
> > source "lib/Kconfig.kfence"
> > +source "lib/Kconfig.kmsan"
> >
> > endmenu # "Memory Debugging"
> >
> > diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
> > new file mode 100644
> > index 0000000000000..199f79d031f94
> > --- /dev/null
> > +++ b/lib/Kconfig.kmsan
> > @@ -0,0 +1,23 @@
>
> Missing SPDX-License-Identifier.
Will do in v4, thanks!
> > +config KMSAN
> > + bool "KMSAN: detector of uninitialized values use"
> > + depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
> > + depends on SLUB && DEBUG_KERNEL && !KASAN && !KCSAN
> > + depends on CC_IS_CLANG && CLANG_VERSION >= 140000
>
> Shouldn't the "CC_IS_CLANG && CLANG_VERSION ..." check be a "depends on"
> in HAVE_KMSAN_COMPILER? That way all the compiler-related checks are
> confined to HAVE_KMSAN_COMPILER.
Good point, thanks!
I also think I can drop the excessive CC_IS_CLANG in the definition of
HAVE_KMSAN_COMPILER.
> I guess, it might also be worth mentioning why the version check is
> required at all (something about older compilers supporting
> fsanitize=kernel-memory, but not having all features we need).
Done.
> > index 0000000000000..a80dde1de7048
> > --- /dev/null
> > +++ b/mm/kmsan/Makefile
> > @@ -0,0 +1,18 @@
>
> Makefile needs a SPDX-License-Identifier.
Done.
> > + shadow_dst = kmsan_get_metadata(dst, KMSAN_META_SHADOW);
> > + if (!shadow_dst)
> > + return;
> > + KMSAN_WARN_ON(!kmsan_metadata_is_contiguous(dst, n));
> > +
> > + shadow_src = kmsan_get_metadata(src, KMSAN_META_SHADOW);
> > + if (!shadow_src) {
> > + /*
> > + * |src| is untracked: zero out destination shadow, ignore the
>
> Probably doesn't matter too much, but for consistency elsewhere - @src?
Fixed here and in other places where |var| is used.
> > + * If |src| isn't aligned on KMSAN_ORIGIN_SIZE, don't
> > + * look at the first |src % KMSAN_ORIGIN_SIZE| bytes
> > + * of the first shadow slot.
> > + */
E.g. here
> > + /*
> > + * If |src + n| isn't aligned on
> > + * KMSAN_ORIGIN_SIZE, don't look at the last
> > + * |(src + n) % KMSAN_ORIGIN_SIZE| bytes of the
> > + * last shadow slot.
> > + */
and here.
> > +
> > +extern bool kmsan_enabled;
> > +extern int panic_on_kmsan;
> > +
> > +/*
> > + * KMSAN performs a lot of consistency checks that are currently enabled by
> > + * default. BUG_ON is normally discouraged in the kernel, unless used for
> > + * debugging, but KMSAN itself is a debugging tool, so it makes little sense to
> > + * recover if something goes wrong.
> > + */
> > +#define KMSAN_WARN_ON(cond) \
> > + ({ \
> > + const bool __cond = WARN_ON(cond); \
> > + if (unlikely(__cond)) { \
> > + WRITE_ONCE(kmsan_enabled, false); \
> > + if (panic_on_kmsan) { \
> > + /* Can't call panic() here because */ \
> > + /* of uaccess checks.*/ \
>
> space after '.'
Done; also reformatted the macro to use tabs instead of spaces.
> > +void kmsan_report(depot_stack_handle_t origin, void *address, int size,
> > + int off_first, int off_last, const void *user_addr,
> > + enum kmsan_bug_reason reason)
> > +{
> > + unsigned long stack_entries[KMSAN_STACK_DEPTH];
> > + int num_stack_entries, skipnr;
> > + char *bug_type = NULL;
> > + unsigned long flags, ua_flags;
> > + bool is_uaf;
> > +
> > + if (!kmsan_enabled)
> > + return;
> > + if (!current->kmsan_ctx.allow_reporting)
> > + return;
> > + if (!origin)
> > + return;
> > +
> > + current->kmsan_ctx.allow_reporting = false;
> > + ua_flags = user_access_save();
> > + spin_lock_irqsave(&kmsan_report_lock, flags);
>
> I think this might want to be a raw_spin_lock, since the reporting can
> be called from any context, including from within other raw_spin_lock'd
> critical sections (practically this will only matter in RT kernels).
(Marco elaborated off-list that lockdep will complain if a spin_lock
critical section is nested inside raw_spin_lock)
Thanks, done.
> Also, do you have to do lockdep_off/on() (like kernel/kcsan/report.c
> does, see comment there)?
I don't see lockdep reports from within mm/kmsan/report.c
However there's one boot-time report that I am struggling to comprehend:
DEBUG_LOCKS_WARN_ON(lockdep_hardirqs_enabled())
WARNING: CPU: 0 PID: 0 at kernel/locking/lockdep.c:5481 check_flags+0x63/0x180
...
<TASK>
lock_acquire+0x85/0x1c0 kernel/locking/lockdep.c:5638
__raw_spin_lock_irqsave ./include/linux/spinlock_api_smp.h:110
_raw_spin_lock_irqsave+0x129/0x220 kernel/locking/spinlock.c:162
__stack_depot_save+0x1b1/0x4b0 lib/stackdepot.c:417
stack_depot_save+0x13/0x20 lib/stackdepot.c:471
__msan_poison_alloca+0x100/0x1a0 mm/kmsan/instrumentation.c:228
_raw_spin_unlock_irqrestore ??:?
arch_local_save_flags ./arch/x86/include/asm/irqflags.h:70
arch_irqs_disabled ./arch/x86/include/asm/irqflags.h:130
__raw_spin_unlock_irqrestore ./include/linux/spinlock_api_smp.h:151
_raw_spin_unlock_irqrestore+0xc6/0x190 kernel/locking/spinlock.c:194
tty_register_ldisc+0x15e/0x1c0 drivers/tty/tty_ldisc.c:68
n_tty_init+0x2f/0x32 drivers/tty/n_tty.c:2418
console_init+0x20/0x10d kernel/printk/printk.c:3220
start_kernel+0x6f0/0xd23 init/main.c:1071
x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:546
x86_64_start_kernel+0xf5/0xfa arch/x86/kernel/head64.c:527
secondary_startup_64_no_verify+0xc4/0xcb ??:?
</TASK>
Perhaps we need to disable lockdep in stackdepot as well?
> > + */
> > +static int kmsan_phys_addr_valid(unsigned long addr)
>
> int -> bool ? (it already deviates from the original by using IS_ENABLED
> instead of #ifdef)
Makes sense.
> > + * Taken from arch/x86/mm/physaddr.c to avoid using an instrumented version.
> > + */
> > +static bool kmsan_virt_addr_valid(void *addr)
> > +{
> > + unsigned long x = (unsigned long)addr;
> > + unsigned long y = x - __START_KERNEL_map;
> > +
> > + /* use the carry flag to determine if x was < __START_KERNEL_map */
> > + if (unlikely(x > y)) {
> > + x = y + phys_base;
> > +
> > + if (y >= KERNEL_IMAGE_SIZE)
> > + return false;
> > + } else {
> > + x = y + (__START_KERNEL_map - PAGE_OFFSET);
> > +
> > + /* carry flag will be set if starting x was >= PAGE_OFFSET */
> > + if ((x > y) || !kmsan_phys_addr_valid(x))
> > + return false;
> > + }
> > +
> > + return pfn_valid(x >> PAGE_SHIFT);
> > +}
>
> These seem quite x86-specific - to ease eventual porting to other
> architectures, it would make sense to introduce <asm/kmsan.h> which will
> have these 2 functions (and if there's anything else arch-specific like
> this, moving to <asm/kmsan.h> would help eventual ports).
Good idea, will do!
This part will probably need to go into "x86: kmsan: enable KMSAN
builds for x86"
> > + if (is_origin && !IS_ALIGNED(addr, KMSAN_ORIGIN_SIZE)) {
> > + pad = addr % KMSAN_ORIGIN_SIZE;
> > + addr -= pad;
> > + }
> > + address = (void *)addr;
> > + if (kmsan_internal_is_vmalloc_addr(address) ||
> > + kmsan_internal_is_module_addr(address))
> > + return (void *)vmalloc_meta(address, is_origin);
> > +
> > + page = virt_to_page_or_null(address);
> > + if (!page)
> > + return NULL;
> > + if (!page_has_metadata(page))
> > + return NULL;
> > + off = addr % PAGE_SIZE;
> > +
> > + ret = (is_origin ? origin_ptr_for(page) : shadow_ptr_for(page)) + off;
>
> Just return this and avoid 'ret'?
Good catch. There was some debugging code in the middle, but now we
don't need ret.
>
> > + return ret;
> > +}
> > diff --git a/scripts/Makefile.kmsan b/scripts/Makefile.kmsan
> > new file mode 100644
> > index 0000000000000..9793591f9855c
> > --- /dev/null
> > +++ b/scripts/Makefile.kmsan
> > @@ -0,0 +1 @@
>
> Makefile.kmsan needs SPDX-License-Identifier.
Done.
--
Alexander Potapenko
Software Engineer
Google Germany GmbH
Erika-Mann-Straße, 33
80636 München
Geschäftsführer: Paul Manicle, Liana Sebastian
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