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Message-Id: <20250206093238.7a716d97b1c31e55a011c591@kernel.org>
Date: Thu, 6 Feb 2025 09:32:38 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Masami
Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton
<akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/8] ring-buffer: Use kaslr address instead of text
delta
On Wed, 05 Feb 2025 17:50:32 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:
> From: Steven Rostedt <rostedt@...dmis.org>
>
> Instead of saving off the text and data pointers and using them to compare
> with the current boot's text and data pointers, just save off the KASLR
> offset. Then that can be used to figure out how to read the previous boots
> buffer.
>
> The last_boot_info will now show this offset, but only if it is for a
> previous boot:
>
> # cat instances/boot_mapped/last_boot_info
> Offset: 39000000
>
> # echo function > instances/boot_mapped/current_tracer
> # cat instances/boot_mapped/last_boot_info
> Offset: current
>
> If the KASLR offset saved is for the current boot, the last_boot_info will
> show the value of "current".
Looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
Thank you!
>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
> include/linux/ring_buffer.h | 3 +--
> kernel/trace/ring_buffer.c | 31 ++++++++++++-------------------
> kernel/trace/trace.c | 30 +++++++++++++++++++++---------
> kernel/trace/trace.h | 9 +++++----
> 4 files changed, 39 insertions(+), 34 deletions(-)
>
> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index 17fbb7855295..8de035f4f0d9 100644
> --- a/include/linux/ring_buffer.h
> +++ b/include/linux/ring_buffer.h
> @@ -94,8 +94,7 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
> unsigned long range_size,
> struct lock_class_key *key);
>
> -bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, long *text,
> - long *data);
> +bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, unsigned long *kaslr_addr);
>
> /*
> * Because the ring buffer is generic, if other users of the ring buffer get
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index b8e0ae15ca5b..7146b780176f 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -31,6 +31,7 @@
>
> #include <asm/local64.h>
> #include <asm/local.h>
> +#include <asm/setup.h>
>
> #include "trace.h"
>
> @@ -49,8 +50,7 @@ static void update_pages_handler(struct work_struct *work);
> struct ring_buffer_meta {
> int magic;
> int struct_size;
> - unsigned long text_addr;
> - unsigned long data_addr;
> + unsigned long kaslr_addr;
> unsigned long first_buffer;
> unsigned long head_buffer;
> unsigned long commit_buffer;
> @@ -550,8 +550,7 @@ struct trace_buffer {
> unsigned long range_addr_start;
> unsigned long range_addr_end;
>
> - long last_text_delta;
> - long last_data_delta;
> + unsigned long kaslr_addr;
>
> unsigned int subbuf_size;
> unsigned int subbuf_order;
> @@ -1874,16 +1873,13 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
> }
> }
>
> -/* Used to calculate data delta */
> -static char rb_data_ptr[] = "";
> -
> -#define THIS_TEXT_PTR ((unsigned long)rb_meta_init_text_addr)
> -#define THIS_DATA_PTR ((unsigned long)rb_data_ptr)
> -
> static void rb_meta_init_text_addr(struct ring_buffer_meta *meta)
> {
> - meta->text_addr = THIS_TEXT_PTR;
> - meta->data_addr = THIS_DATA_PTR;
> +#ifdef CONFIG_RANDOMIZE_BASE
> + meta->kaslr_addr = kaslr_offset();
> +#else
> + meta->kaslr_addr = 0;
> +#endif
> }
>
> static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages)
> @@ -1906,8 +1902,7 @@ static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages)
> meta->first_buffer += delta;
> meta->head_buffer += delta;
> meta->commit_buffer += delta;
> - buffer->last_text_delta = THIS_TEXT_PTR - meta->text_addr;
> - buffer->last_data_delta = THIS_DATA_PTR - meta->data_addr;
> + buffer->kaslr_addr = meta->kaslr_addr;
> continue;
> }
>
> @@ -2459,17 +2454,15 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
> *
> * Returns: The true if the delta is non zero
> */
> -bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, long *text,
> - long *data)
> +bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, unsigned long *kaslr_addr)
> {
> if (!buffer)
> return false;
>
> - if (!buffer->last_text_delta)
> + if (!buffer->kaslr_addr)
> return false;
>
> - *text = buffer->last_text_delta;
> - *data = buffer->last_data_delta;
> + *kaslr_addr = buffer->kaslr_addr;
>
> return true;
> }
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 1496a5ac33ae..a9e8eaf1d47e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -50,7 +50,7 @@
> #include <linux/irq_work.h>
> #include <linux/workqueue.h>
>
> -#include <asm/setup.h> /* COMMAND_LINE_SIZE */
> +#include <asm/setup.h> /* COMMAND_LINE_SIZE and kaslr_offset() */
>
> #include "trace.h"
> #include "trace_output.h"
> @@ -4193,7 +4193,7 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
> * safe to use if the array has delta offsets
> * Force printing via the fields.
> */
> - if ((tr->text_delta || tr->data_delta) &&
> + if ((tr->text_delta) &&
> event->type > __TRACE_LAST_TYPE)
> return print_event_fields(iter, event);
>
> @@ -5996,7 +5996,7 @@ ssize_t tracing_resize_ring_buffer(struct trace_array *tr,
>
> static void update_last_data(struct trace_array *tr)
> {
> - if (!tr->text_delta && !tr->data_delta)
> + if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
> return;
>
> /*
> @@ -6009,7 +6009,8 @@ static void update_last_data(struct trace_array *tr)
>
> /* Using current data now */
> tr->text_delta = 0;
> - tr->data_delta = 0;
> +
> + tr->flags &= ~TRACE_ARRAY_FL_LAST_BOOT;
> }
>
> /**
> @@ -6827,8 +6828,17 @@ tracing_last_boot_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t
>
> seq_buf_init(&seq, buf, 64);
>
> - seq_buf_printf(&seq, "text delta:\t%ld\n", tr->text_delta);
> - seq_buf_printf(&seq, "data delta:\t%ld\n", tr->data_delta);
> + /*
> + * Do not leak KASLR address. This only shows the KASLR address of
> + * the last boot. When the ring buffer is started, the LAST_BOOT
> + * flag gets cleared, and this should only report "current".
> + * Otherwise it shows the KASLR address from the previous boot which
> + * should not be the same as the current boot.
> + */
> + if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
> + seq_buf_puts(&seq, "Offset: current\n");
> + else
> + seq_buf_printf(&seq, "Offset: %lx\n", tr->kaslr_addr);
>
> return simple_read_from_buffer(ubuf, cnt, ppos, buf, seq_buf_used(&seq));
> }
> @@ -9212,8 +9222,10 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size
> tr->range_addr_start,
> tr->range_addr_size);
>
> - ring_buffer_last_boot_delta(buf->buffer,
> - &tr->text_delta, &tr->data_delta);
> +#ifdef CONFIG_RANDOMIZE_BASE
> + if (ring_buffer_last_boot_delta(buf->buffer, &tr->kaslr_addr))
> + tr->text_delta = kaslr_offset() - tr->kaslr_addr;
> +#endif
> /*
> * This is basically the same as a mapped buffer,
> * with the same restrictions.
> @@ -10461,7 +10473,7 @@ __init static void enable_instances(void)
> * to it.
> */
> if (start) {
> - tr->flags |= TRACE_ARRAY_FL_BOOT;
> + tr->flags |= TRACE_ARRAY_FL_BOOT | TRACE_ARRAY_FL_LAST_BOOT;
> tr->ref++;
> }
>
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 9c21ba45b7af..abe8169c3e87 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -348,8 +348,8 @@ struct trace_array {
> unsigned int mapped;
> unsigned long range_addr_start;
> unsigned long range_addr_size;
> + unsigned long kaslr_addr;
> long text_delta;
> - long data_delta;
>
> struct trace_pid_list __rcu *filtered_pids;
> struct trace_pid_list __rcu *filtered_no_pids;
> @@ -433,9 +433,10 @@ struct trace_array {
> };
>
> enum {
> - TRACE_ARRAY_FL_GLOBAL = BIT(0),
> - TRACE_ARRAY_FL_BOOT = BIT(1),
> - TRACE_ARRAY_FL_MOD_INIT = BIT(2),
> + TRACE_ARRAY_FL_GLOBAL = BIT(0),
> + TRACE_ARRAY_FL_BOOT = BIT(1),
> + TRACE_ARRAY_FL_LAST_BOOT = BIT(2),
> + TRACE_ARRAY_FL_MOD_INIT = BIT(3),
> };
>
> #ifdef CONFIG_MODULES
> --
> 2.45.2
>
>
--
Masami Hiramatsu (Google) <mhiramat@...nel.org>
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