2024-02-14 15:44:15

by Steven Rostedt

Subject: [PATCH] tracing: Inform kmemleak of saved_cmdlines allocation

From: "Steven Rostedt (Google)" <[email protected]>

The allocation of the struct saved_cmdlines_buffer structure changed from:

s = kmalloc(sizeof(*s), GFP_KERNEL);
s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL);

to:

orig_size = sizeof(*s) + val * TASK_COMM_LEN;
order = get_order(orig_size);
size = 1 << (order + PAGE_SHIFT);
page = alloc_pages(GFP_KERNEL, order);
if (!page)
return NULL;

s = page_address(page);
memset(s, 0, sizeof(*s));

s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL);

Where that s->saved_cmdlines allocation looks to be a dangling allocation
to kmemleak. That's because kmemleak only keeps track of kmalloc()
allocations. For allocations that use page_alloc() directly, the kmemleak
needs to be explicitly informed about it.

Add kmemleak_alloc() and kmemleak_free() around the page allocation so
that it doesn't give the following false positive:

unreferenced object 0xffff8881010c8000 (size 32760):
comm "swapper", pid 0, jiffies 4294667296
hex dump (first 32 bytes):
ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
backtrace (crc ae6ec1b9):
[<ffffffff86722405>] kmemleak_alloc+0x45/0x80
[<ffffffff8414028d>] __kmalloc_large_node+0x10d/0x190
[<ffffffff84146ab1>] __kmalloc+0x3b1/0x4c0
[<ffffffff83ed7103>] allocate_cmdlines_buffer+0x113/0x230
[<ffffffff88649c34>] tracer_alloc_buffers.isra.0+0x124/0x460
[<ffffffff8864a174>] early_trace_init+0x14/0xa0
[<ffffffff885dd5ae>] start_kernel+0x12e/0x3c0
[<ffffffff885f5758>] x86_64_start_reservations+0x18/0x30
[<ffffffff885f582b>] x86_64_start_kernel+0x7b/0x80
[<ffffffff83a001c3>] secondary_startup_64_no_verify+0x15e/0x16b

Link: https://lore.kernel.org/linux-trace-kernel/[email protected]/

Fixes: 44dc5c41b5b1 ("tracing: Fix wasted memory in saved_cmdlines logic")
Reported-by: Kalle Valo <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>
---
kernel/trace/trace_sched_switch.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index e4fbcc3bede5..de4182224ea2 100644
--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -9,6 +9,7 @@
#include <linux/kallsyms.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
+#include <linux/kmemleak.h>
#include <trace/events/sched.h>

#include "trace.h"
@@ -190,6 +191,7 @@ static void free_saved_cmdlines_buffer(struct saved_cmdlines_buffer *s)
int order = get_order(sizeof(*s) + s->cmdline_num * TASK_COMM_LEN);

kfree(s->map_cmdline_to_pid);
+ kmemleak_free(s);
free_pages((unsigned long)s, order);
}

@@ -210,6 +212,7 @@ static struct saved_cmdlines_buffer *allocate_cmdlines_buffer(unsigned int val)

s = page_address(page);
memset(s, 0, sizeof(*s));
+ kmemleak_alloc(s, size, 1, GFP_KERNEL);

/* Round up to actual allocation */
val = (size - sizeof(*s)) / TASK_COMM_LEN;
--
2.43.0

2024-02-19 11:50:31

by Catalin Marinas

Subject: Re: [PATCH] tracing: Inform kmemleak of saved_cmdlines allocation

On Wed, Feb 14, 2024 at 10:26:14AM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <[email protected]>
>
> The allocation of the struct saved_cmdlines_buffer structure changed from:
>
> s = kmalloc(sizeof(*s), GFP_KERNEL);
> s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL);
>
> to:
>
> orig_size = sizeof(*s) + val * TASK_COMM_LEN;
> order = get_order(orig_size);
> size = 1 << (order + PAGE_SHIFT);
> page = alloc_pages(GFP_KERNEL, order);
> if (!page)
> return NULL;
>
> s = page_address(page);
> memset(s, 0, sizeof(*s));
>
> s->saved_cmdlines = kmalloc_array(TASK_COMM_LEN, val, GFP_KERNEL);
>
> Where that s->saved_cmdlines allocation looks to be a dangling allocation
> to kmemleak. That's because kmemleak only keeps track of kmalloc()
> allocations. For allocations that use page_alloc() directly, the kmemleak
> needs to be explicitly informed about it.
>
> Add kmemleak_alloc() and kmemleak_free() around the page allocation so
> that it doesn't give the following false positive:
>
> unreferenced object 0xffff8881010c8000 (size 32760):
> comm "swapper", pid 0, jiffies 4294667296
> hex dump (first 32 bytes):
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
> ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
> backtrace (crc ae6ec1b9):
> [<ffffffff86722405>] kmemleak_alloc+0x45/0x80
> [<ffffffff8414028d>] __kmalloc_large_node+0x10d/0x190
> [<ffffffff84146ab1>] __kmalloc+0x3b1/0x4c0
> [<ffffffff83ed7103>] allocate_cmdlines_buffer+0x113/0x230
> [<ffffffff88649c34>] tracer_alloc_buffers.isra.0+0x124/0x460
> [<ffffffff8864a174>] early_trace_init+0x14/0xa0
> [<ffffffff885dd5ae>] start_kernel+0x12e/0x3c0
> [<ffffffff885f5758>] x86_64_start_reservations+0x18/0x30
> [<ffffffff885f582b>] x86_64_start_kernel+0x7b/0x80
> [<ffffffff83a001c3>] secondary_startup_64_no_verify+0x15e/0x16b
>
> Link: https://lore.kernel.org/linux-trace-kernel/[email protected]/
>
> Fixes: 44dc5c41b5b1 ("tracing: Fix wasted memory in saved_cmdlines logic")
> Reported-by: Kalle Valo <[email protected]>
> Signed-off-by: Steven Rostedt (Google) <[email protected]>

Reviewed-by: Catalin Marinas <[email protected]>