Re: [PATCH 4/8] tracing: Have persistent trace instances save KASLR offset

From: Google
Date: Thu Feb 06 2025 - 00:23:11 EST

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In reply to: Steven Rostedt: "[PATCH 4/8] tracing: Have persistent trace instances save KASLR offset"
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On Wed, 05 Feb 2025 17:50:35 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> From: Steven Rostedt <rostedt@xxxxxxxxxxx>
>
> There's no reason to save the KASLR offset for the ring buffer itself.
> That is used by the tracer. Now that the tracer has a way to save data in
> the persistent memory of the ring buffer, have the tracing infrastructure
> take care of the saving of the KASLR offset.
>

Looks good to me. But note that the scratchpad size may not enough for
module table later, because 1 module requires at least the name[]
(64byte - sizeof(ulong)) and the base address (ulong). This means
1 entry consumes 64byte. Thus there can be only 63 entries + meta
data in 4K page. My ubuntu loads 189(!) modules;

$ lsmod | wc -l
190

so we want 255 entries, which requires 16KB.

Thank you,

> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
> include/linux/ring_buffer.h | 1 -
> kernel/trace/ring_buffer.c | 47 -------------------------------------
> kernel/trace/trace.c | 38 ++++++++++++++++++++++++++----
> kernel/trace/trace.h | 6 +++--
> 4 files changed, 38 insertions(+), 54 deletions(-)
>
> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
> index b95f940fd07a..d6d9c94e8d8a 100644
> --- a/include/linux/ring_buffer.h
> +++ b/include/linux/ring_buffer.h
> @@ -94,7 +94,6 @@ 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, unsigned long *kaslr_addr);
> void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size);
>
> /*
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 5a81ff785665..a42406287281 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -55,7 +55,6 @@ struct ring_buffer_meta {
> };
>
> struct ring_buffer_cpu_meta {
> - unsigned long kaslr_addr;
> unsigned long first_buffer;
> unsigned long head_buffer;
> unsigned long commit_buffer;
> @@ -557,8 +556,6 @@ struct trace_buffer {
>
> struct ring_buffer_meta *meta;
>
> - unsigned long kaslr_addr;
> -
> unsigned int subbuf_size;
> unsigned int subbuf_order;
> unsigned int max_data_size;
> @@ -1931,15 +1928,6 @@ static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
> }
> }
>
> -static void rb_meta_init_text_addr(struct ring_buffer_cpu_meta *meta)
> -{
> -#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)
> {
> struct ring_buffer_cpu_meta *meta;
> @@ -1967,7 +1955,6 @@ 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->kaslr_addr = meta->kaslr_addr;
> continue;
> }
>
> @@ -1984,7 +1971,6 @@ static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages)
> subbuf = rb_subbufs_from_meta(meta);
>
> meta->first_buffer = (unsigned long)subbuf;
> - rb_meta_init_text_addr(meta);
>
> /*
> * The buffers[] array holds the order of the sub-buffers
> @@ -2514,27 +2500,6 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag
> return alloc_buffer(size, flags, order, start, start + range_size, key);
> }
>
> -/**
> - * ring_buffer_last_boot_delta - return the delta offset from last boot
> - * @buffer: The buffer to return the delta from
> - * @text: Return text delta
> - * @data: Return data delta
> - *
> - * Returns: The true if the delta is non zero
> - */
> -bool ring_buffer_last_boot_delta(struct trace_buffer *buffer, unsigned long *kaslr_addr)
> -{
> - if (!buffer)
> - return false;
> -
> - if (!buffer->kaslr_addr)
> - return false;
> -
> - *kaslr_addr = buffer->kaslr_addr;
> -
> - return true;
> -}
> -
> void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size)
> {
> if (!buffer || !buffer->meta)
> @@ -6098,7 +6063,6 @@ static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
> void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
> {
> struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
> - struct ring_buffer_cpu_meta *meta;
>
> if (!cpumask_test_cpu(cpu, buffer->cpumask))
> return;
> @@ -6117,11 +6081,6 @@ void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
> atomic_dec(&cpu_buffer->record_disabled);
> atomic_dec(&cpu_buffer->resize_disabled);
>
> - /* Make sure persistent meta now uses this buffer's addresses */
> - meta = rb_range_meta(buffer, 0, cpu_buffer->cpu);
> - if (meta)
> - rb_meta_init_text_addr(meta);
> -
> mutex_unlock(&buffer->mutex);
> }
> EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
> @@ -6136,7 +6095,6 @@ EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
> void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
> {
> struct ring_buffer_per_cpu *cpu_buffer;
> - struct ring_buffer_cpu_meta *meta;
> int cpu;
>
> /* prevent another thread from changing buffer sizes */
> @@ -6164,11 +6122,6 @@ void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
>
> reset_disabled_cpu_buffer(cpu_buffer);
>
> - /* Make sure persistent meta now uses this buffer's addresses */
> - meta = rb_range_meta(buffer, 0, cpu_buffer->cpu);
> - if (meta)
> - rb_meta_init_text_addr(meta);
> -
> atomic_dec(&cpu_buffer->record_disabled);
> atomic_sub(RESET_BIT, &cpu_buffer->resize_disabled);
> }
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a9e8eaf1d47e..cb9f8e6878a0 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5994,8 +5994,14 @@ ssize_t tracing_resize_ring_buffer(struct trace_array *tr,
> return ret;
> }
>
> +struct trace_scratch {
> + unsigned long kaslr_addr;
> +};
> +
> static void update_last_data(struct trace_array *tr)
> {
> + struct trace_scratch *tscratch;
> +
> if (!(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
> return;
>
> @@ -6010,6 +6016,17 @@ static void update_last_data(struct trace_array *tr)
> /* Using current data now */
> tr->text_delta = 0;
>
> + if (!tr->scratch)
> + return;
> +
> + tscratch = tr->scratch;
> +
> + /* Set the persistent ring buffer meta data to this address */
> +#ifdef CONFIG_RANDOMIZE_BASE
> + tscratch->kaslr_addr = kaslr_offset();
> +#else
> + tscratch->kaslr_addr = 0;
> +#endif
> tr->flags &= ~TRACE_ARRAY_FL_LAST_BOOT;
> }
>
> @@ -6823,6 +6840,7 @@ static ssize_t
> tracing_last_boot_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
> {
> struct trace_array *tr = filp->private_data;
> + struct trace_scratch *tscratch = tr->scratch;
> struct seq_buf seq;
> char buf[64];
>
> @@ -6835,10 +6853,10 @@ tracing_last_boot_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t
> * 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))
> + if (!tscratch || !(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);
> + seq_buf_printf(&seq, "Offset: %lx\n", tscratch->kaslr_addr);
>
> return simple_read_from_buffer(ubuf, cnt, ppos, buf, seq_buf_used(&seq));
> }
> @@ -9212,6 +9230,8 @@ static int
> allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size)
> {
> enum ring_buffer_flags rb_flags;
> + unsigned int scratch_size;
> + void *scratch;
>
> rb_flags = tr->trace_flags & TRACE_ITER_OVERWRITE ? RB_FL_OVERWRITE : 0;
>
> @@ -9222,10 +9242,20 @@ allocate_trace_buffer(struct trace_array *tr, struct array_buffer *buf, int size
> tr->range_addr_start,
> tr->range_addr_size);
>
> + scratch = ring_buffer_meta_scratch(buf->buffer, &scratch_size);
> + if (scratch) {
> + tr->scratch = scratch;
> + tr->scratch_size = scratch_size;
> +
> #ifdef CONFIG_RANDOMIZE_BASE
> - if (ring_buffer_last_boot_delta(buf->buffer, &tr->kaslr_addr))
> - tr->text_delta = kaslr_offset() - tr->kaslr_addr;
> + {
> + struct trace_scratch *tscratch = tr->scratch;
> +
> + if (tscratch->kaslr_addr)
> + tr->text_delta = kaslr_offset() - tscratch->kaslr_addr;
> + }
> #endif
> + }
> /*
> * This is basically the same as a mapped buffer,
> * with the same restrictions.
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index abe8169c3e87..3a020fb82a34 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -348,8 +348,11 @@ struct trace_array {
> unsigned int mapped;
> unsigned long range_addr_start;
> unsigned long range_addr_size;
> - unsigned long kaslr_addr;
> long text_delta;
> + void *scratch; /* pointer in persistent memory */
> + int scratch_size;
> +
> + int buffer_disabled;
>
> struct trace_pid_list __rcu *filtered_pids;
> struct trace_pid_list __rcu *filtered_no_pids;
> @@ -367,7 +370,6 @@ struct trace_array {
> * CONFIG_TRACER_MAX_TRACE.
> */
> arch_spinlock_t max_lock;
> - int buffer_disabled;
> #ifdef CONFIG_FTRACE_SYSCALLS
> int sys_refcount_enter;
> int sys_refcount_exit;
> --
> 2.45.2
>
>

--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Next message: Armin Wolf: "Re: [PATCH v8 00/14] platform/x86: alienware-wmi driver rework"
Previous message: Harshit Mogalapalli: "Re: [PATCH 6.6 000/393] 6.6.76-rc1 review"
In reply to: Steven Rostedt: "[PATCH 4/8] tracing: Have persistent trace instances save KASLR offset"
Next in thread: Steven Rostedt: "Re: [PATCH 4/8] tracing: Have persistent trace instances save KASLR offset"
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