From 6cae637fa26df867449c6bc20ea8bc693abe49b0 Mon Sep 17 00:00:00 2001
From: Alexander Potapenko <glider@google.com>
Date: Thu, 15 Sep 2022 17:04:14 +0200
Subject: [PATCH] entry: kmsan: introduce kmsan_unpoison_entry_regs()
struct pt_regs passed into IRQ entry code is set up by uninstrumented asm
functions, therefore KMSAN may not notice the registers are initialized.
kmsan_unpoison_entry_regs() unpoisons the contents of struct pt_regs,
preventing potential false positives. Unlike kmsan_unpoison_memory(), it
can be called under kmsan_in_runtime(), which is often the case in IRQ
entry code.
Link: https://lkml.kernel.org/r/20220915150417.722975-41-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
include/linux/kmsan.h | 15 +++++++++++++++
kernel/entry/common.c | 5 +++++
mm/kmsan/hooks.c | 26 ++++++++++++++++++++++++++
3 files changed, 46 insertions(+)
diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
index c473e0e21683c..e38ae3c346184 100644
--- a/include/linux/kmsan.h
+++ b/include/linux/kmsan.h
@@ -214,6 +214,17 @@ void kmsan_handle_dma_sg(struct scatterlist *sg, int nents,
*/
void kmsan_handle_urb(const struct urb *urb, bool is_out);
+/**
+ * kmsan_unpoison_entry_regs() - Handle pt_regs in low-level entry code.
+ * @regs: struct pt_regs pointer received from assembly code.
+ *
+ * KMSAN unpoisons the contents of the passed pt_regs, preventing potential
+ * false positive reports. Unlike kmsan_unpoison_memory(),
+ * kmsan_unpoison_entry_regs() can be called from the regions where
+ * kmsan_in_runtime() returns true, which is the case in early entry code.
+ */
+void kmsan_unpoison_entry_regs(const struct pt_regs *regs);
+
#else
static inline void kmsan_init_shadow(void)
@@ -310,6 +321,10 @@ static inline void kmsan_handle_urb(const struct urb *urb, bool is_out)
{
}
+static inline void kmsan_unpoison_entry_regs(const struct pt_regs *regs)
+{
+}
+
#endif
#endif /* _LINUX_KMSAN_H */
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 063068a9ea9b3..846add8394c41 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -5,6 +5,7 @@
#include <linux/resume_user_mode.h>
#include <linux/highmem.h>
#include <linux/jump_label.h>
+#include <linux/kmsan.h>
#include <linux/livepatch.h>
#include <linux/audit.h>
#include <linux/tick.h>
@@ -24,6 +25,7 @@ static __always_inline void __enter_from_user_mode(struct pt_regs *regs)
user_exit_irqoff();
instrumentation_begin();
+ kmsan_unpoison_entry_regs(regs);
trace_hardirqs_off_finish();
instrumentation_end();
}
@@ -352,6 +354,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
lockdep_hardirqs_off(CALLER_ADDR0);
ct_irq_enter();
instrumentation_begin();
+ kmsan_unpoison_entry_regs(regs);
trace_hardirqs_off_finish();
instrumentation_end();
@@ -367,6 +370,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
*/
lockdep_hardirqs_off(CALLER_ADDR0);
instrumentation_begin();
+ kmsan_unpoison_entry_regs(regs);
rcu_irq_enter_check_tick();
trace_hardirqs_off_finish();
instrumentation_end();
@@ -452,6 +456,7 @@ irqentry_state_t noinstr irqentry_nmi_enter(struct pt_regs *regs)
ct_nmi_enter();
instrumentation_begin();
+ kmsan_unpoison_entry_regs(regs);
trace_hardirqs_off_finish();
ftrace_nmi_enter();
instrumentation_end();
diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 79d7e73e2cfd8..35f6b6e6a908c 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -348,6 +348,32 @@ void kmsan_unpoison_memory(const void *address, size_t size)
}
EXPORT_SYMBOL(kmsan_unpoison_memory);
+/*
+ * Version of kmsan_unpoison_memory() that can be called from within the KMSAN
+ * runtime.
+ *
+ * Non-instrumented IRQ entry functions receive struct pt_regs from assembly
+ * code. Those regs need to be unpoisoned, otherwise using them will result in
+ * false positives.
+ * Using kmsan_unpoison_memory() is not an option in entry code, because the
+ * return value of in_task() is inconsistent - as a result, certain calls to
+ * kmsan_unpoison_memory() are ignored. kmsan_unpoison_entry_regs() ensures that
+ * the registers are unpoisoned even if kmsan_in_runtime() is true in the early
+ * entry code.
+ */
+void kmsan_unpoison_entry_regs(const struct pt_regs *regs)
+{
+ unsigned long ua_flags;
+
+ if (!kmsan_enabled)
+ return;
+
+ ua_flags = user_access_save();
+ kmsan_internal_unpoison_memory((void *)regs, sizeof(*regs),
+ KMSAN_POISON_NOCHECK);
+ user_access_restore(ua_flags);
+}
+
void kmsan_check_memory(const void *addr, size_t size)
{
if (!kmsan_enabled)
--
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