android-5.4/UPSTREAM-rss_stat-Add-support-to-detect-RSS-updates-of-external-mm.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Joel Fernandes <joelaf@google.com>
Date: Mon, 18 Nov 2019 14:02:15 -0500
Subject: UPSTREAM: rss_stat: Add support to detect RSS updates of external mm

When a process updates the RSS of a different process, the rss_stat
tracepoint appears in the context of the process doing the update. This
can confuse userspace that the RSS of process doing the update is
updated, while in reality a different process's RSS was updated.

This issue happens in reclaim paths such as with direct reclaim or
background reclaim.

This patch adds more information to the tracepoint about whether the mm
being updated belongs to the current process's context (curr field). We
also include a hash of the mm pointer so that the process who the mm
belongs to can be uniquely identified (mm_id field).

Also vsprintf.c is refactored a bit to allow reuse of hashing code.

Change-Id: Ic87af93af608c83be0b08757aed99d2b9c2c01d8
Reported-by: Ioannis Ilkos <ilkos@google.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Acked-by: Petr Mladek <pmladek@suse.com> # lib/vsprintf.c
Signed-off-by: Joel Fernandes <joelaf@google.com>
---
 include/linux/mm.h          |  8 ++++----
 include/linux/string.h      |  2 ++
 include/trace/events/kmem.h | 32 +++++++++++++++++++++++++++++---
 lib/vsprintf.c              | 35 ++++++++++++++++++++++++-----------
 mm/memory.c                 |  4 ++--
 5 files changed, 61 insertions(+), 20 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7cf998f7b1bc..265ee4ac4d7a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1643,27 +1643,27 @@ static inline unsigned long get_mm_counter(struct mm_struct *mm, int member)
 	return (unsigned long)val;
 }
 
-void mm_trace_rss_stat(int member, long count);
+void mm_trace_rss_stat(struct mm_struct *mm, int member, long count);
 
 static inline void add_mm_counter(struct mm_struct *mm, int member, long value)
 {
 	long count = atomic_long_add_return(value, &mm->rss_stat.count[member]);
 
-	mm_trace_rss_stat(member, count);
+	mm_trace_rss_stat(mm, member, count);
 }
 
 static inline void inc_mm_counter(struct mm_struct *mm, int member)
 {
 	long count = atomic_long_inc_return(&mm->rss_stat.count[member]);
 
-	mm_trace_rss_stat(member, count);
+	mm_trace_rss_stat(mm, member, count);
 }
 
 static inline void dec_mm_counter(struct mm_struct *mm, int member)
 {
 	long count = atomic_long_dec_return(&mm->rss_stat.count[member]);
 
-	mm_trace_rss_stat(member, count);
+	mm_trace_rss_stat(mm, member, count);
 }
 
 /* Optimized variant when page is already known not to be PageAnon */
diff --git a/include/linux/string.h b/include/linux/string.h
index b6ccdc2c7f02..02894e417565 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -216,6 +216,8 @@ int bprintf(u32 *bin_buf, size_t size, const char *fmt, ...) __printf(3, 4);
 extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
 				       const void *from, size_t available);
 
+int ptr_to_hashval(const void *ptr, unsigned long *hashval_out);
+
 /**
  * strstarts - does @str start with @prefix?
  * @str: string to examine
diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
index 5a0666bfcf85..ad7e642bd497 100644
--- a/include/trace/events/kmem.h
+++ b/include/trace/events/kmem.h
@@ -316,24 +316,50 @@ TRACE_EVENT(mm_page_alloc_extfrag,
 		__entry->change_ownership)
 );
 
+/*
+ * Required for uniquely and securely identifying mm in rss_stat tracepoint.
+ */
+#ifndef __PTR_TO_HASHVAL
+static unsigned int __maybe_unused mm_ptr_to_hash(const void *ptr)
+{
+	int ret;
+	unsigned long hashval;
+
+	ret = ptr_to_hashval(ptr, &hashval);
+	if (ret)
+		return 0;
+
+	/* The hashed value is only 32-bit */
+	return (unsigned int)hashval;
+}
+#define __PTR_TO_HASHVAL
+#endif
+
 TRACE_EVENT(rss_stat,
 
-	TP_PROTO(int member,
+	TP_PROTO(struct mm_struct *mm,
+		int member,
 		long count),
 
-	TP_ARGS(member, count),
+	TP_ARGS(mm, member, count),
 
 	TP_STRUCT__entry(
+		__field(unsigned int, mm_id)
+		__field(unsigned int, curr)
 		__field(int, member)
 		__field(long, size)
 	),
 
 	TP_fast_assign(
+		__entry->mm_id = mm_ptr_to_hash(mm);
+		__entry->curr = !!(current->mm == mm);
 		__entry->member = member;
 		__entry->size = (count << PAGE_SHIFT);
 	),
 
-	TP_printk("member=%d size=%ldB",
+	TP_printk("mm_id=%u curr=%d member=%d size=%ldB",
+		__entry->mm_id,
+		__entry->curr,
 		__entry->member,
 		__entry->size)
 	);
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index e78017a3e1bd..465c5758d222 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -738,6 +738,27 @@ static int __init initialize_ptr_random(void)
 	return ret;
 }
 early_initcall(initialize_ptr_random);
+ 
+int ptr_to_hashval(const void *ptr, unsigned long *hashval_out)
+{
+	unsigned long hashval;
+
+	if (static_branch_unlikely(&not_filled_random_ptr_key))
+		return -EAGAIN;
+
+#ifdef CONFIG_64BIT
+	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
+	/*
+	 * Mask off the first 32 bits, this makes explicit that we have
+	 * modified the address (and 32 bits is plenty for a unique ID).
+	 */
+	hashval = hashval & 0xffffffff;
+#else
+	hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key);
+#endif
+	*hashval_out = hashval;
+	return 0;
+}
 
 /* Maps a pointer to a 32 bit unique identifier. */
 static char *ptr_to_id(char *buf, char *end, const void *ptr,
@@ -745,6 +766,7 @@ static char *ptr_to_id(char *buf, char *end, const void *ptr,
 {
 	const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)";
 	unsigned long hashval;
+	int ret;
 
 	/* When debugging early boot use non-cryptographically secure hash. */
 	if (unlikely(debug_boot_weak_hash)) {
@@ -752,22 +774,13 @@ static char *ptr_to_id(char *buf, char *end, const void *ptr,
 		return pointer_string(buf, end, (const void *)hashval, spec);
 	}
 
-	if (static_branch_unlikely(&not_filled_random_ptr_key)) {
+	ret = ptr_to_hashval(ptr, &hashval);
+	if (ret) {
 		spec.field_width = 2 * sizeof(ptr);
 		/* string length must be less than default_width */
 		return error_string(buf, end, str, spec);
 	}
 
-#ifdef CONFIG_64BIT
-	hashval = (unsigned long)siphash_1u64((u64)ptr, &ptr_key);
-	/*
-	 * Mask off the first 32 bits, this makes explicit that we have
-	 * modified the address (and 32 bits is plenty for a unique ID).
-	 */
-	hashval = hashval & 0xffffffff;
-#else
-	hashval = (unsigned long)siphash_1u32((u32)ptr, &ptr_key);
-#endif
 	return pointer_string(buf, end, (const void *)hashval, spec);
 }
 
diff --git a/mm/memory.c b/mm/memory.c
index 499b1916a6b6..3fb5bad0b262 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -142,9 +142,9 @@ static int __init init_zero_pfn(void)
 }
 core_initcall(init_zero_pfn);
 
-void mm_trace_rss_stat(int member, long count)
+void mm_trace_rss_stat(struct mm_struct *mm, int member, long count)
 {
-	trace_rss_stat(member, count);
+	trace_rss_stat(mm, member, count);
 }
 
 #if defined(SPLIT_RSS_COUNTING)