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Date: Sun, 5 May 2024 17:24:55 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Erick Archer <erick.archer@...look.com>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
"Liang, Kan" <kan.liang@...ux.intel.com>, Kees Cook <keescook@...omium.org>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
<morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v2] perf/ring_buffer: Prefer struct_size over open coded
arithmetic
Le 05/05/2024 à 16:15, Erick Archer a écrit :
> This is an effort to get rid of all multiplications from allocation
> functions in order to prevent integer overflows [1][2].
>
> As the "rb" variable is a pointer to "struct perf_buffer" and this
> structure ends in a flexible array:
>
> struct perf_buffer {
> [...]
> void *data_pages[];
> };
>
> the preferred way in the kernel is to use the struct_size() helper to
> do the arithmetic instead of the calculation "size + count * size" in
> the kzalloc_node() functions.
>
> In the "rb_alloc" function defined in the else branch of the macro
>
> #ifndef CONFIG_PERF_USE_VMALLOC
>
> the count in the struct_size helper is the literal "1" since only one
> pointer to void is allocated. Also, remove the "size" variable as it
> is no longer needed.
>
> At the same time, prepare for the coming implementation by GCC and Clang
> of the __counted_by attribute. Flexible array members annotated with
> __counted_by can have their accesses bounds-checked at run-time via
> CONFIG_UBSAN_BOUNDS (for array indexing) and CONFIG_FORTIFY_SOURCE (for
> strcpy/memcpy-family functions). In this case, it is important to note
> that the logic needs a little refactoring to ensure that the "nr_pages"
> member is initialized before the first access to the flex array.
>
> In one case, it is only necessary to move the assignment before the
> array-writing loop while in the other case the assignment needs to be
> added.
>
> This way, the code is more safer.
>
> This code was detected with the help of Coccinelle, and audited and
> modified manually.
>
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
> Link: https://github.com/KSPP/linux/issues/160 [2]
> Signed-off-by: Erick Archer <erick.archer@...look.com>
> ---
> Changes in v2:
> - Annotate "struct perf_buffer" with __counted_by() attribute (Kees Cook).
> - Refactor the logic to gain __counted_by() coverage (Kees Cook).
>
> Previous versions:
> v1 -> https://lore.kernel.org/linux-hardening/AS8PR02MB72372AB065EA8340D960CCC48B1B2@AS8PR02MB7237.eurprd02.prod.outlook.com/
>
> Hi Peter,
>
> I know that you detest the struct_size() helper, however, as Kees
> explained in v1, this change improves the robustness of the code.
> Also, we will gain __counted_by() coverage.
>
> I hope this patch can be applied this time.
>
> Regards,
> Erick
> ---
> kernel/events/internal.h | 2 +-
> kernel/events/ring_buffer.c | 14 ++++----------
> 2 files changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/events/internal.h b/kernel/events/internal.h
> index 5150d5f84c03..dc8d39b01adb 100644
> --- a/kernel/events/internal.h
> +++ b/kernel/events/internal.h
> @@ -55,7 +55,7 @@ struct perf_buffer {
> void *aux_priv;
>
> struct perf_event_mmap_page *user_page;
> - void *data_pages[];
> + void *data_pages[] __counted_by(nr_pages);
> };
>
> extern void rb_free(struct perf_buffer *rb);
> diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
> index 4013408ce012..080537eff69f 100644
> --- a/kernel/events/ring_buffer.c
> +++ b/kernel/events/ring_buffer.c
> @@ -822,9 +822,7 @@ struct perf_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
> unsigned long size;
Hi,
Should size be size_t?
> int i, node;
>
> - size = sizeof(struct perf_buffer);
> - size += nr_pages * sizeof(void *);
> -
> + size = struct_size(rb, data_pages, nr_pages);
> if (order_base_2(size) > PAGE_SHIFT+MAX_PAGE_ORDER)
> goto fail;
>
> @@ -833,6 +831,7 @@ struct perf_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
> if (!rb)
> goto fail;
>
> + rb->nr_pages = nr_pages;
> rb->user_page = perf_mmap_alloc_page(cpu);
> if (!rb->user_page)
> goto fail_user_page;
> @@ -843,8 +842,6 @@ struct perf_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
> goto fail_data_pages;
> }
>
> - rb->nr_pages = nr_pages;
> -
> ring_buffer_init(rb, watermark, flags);
>
> return rb;
> @@ -916,18 +913,15 @@ void rb_free(struct perf_buffer *rb)
> struct perf_buffer *rb_alloc(int nr_pages, long watermark, int cpu, int flags)
> {
> struct perf_buffer *rb;
> - unsigned long size;
> void *all_buf;
> int node;
>
> - size = sizeof(struct perf_buffer);
> - size += sizeof(void *);
> -
> node = (cpu == -1) ? cpu : cpu_to_node(cpu);
> - rb = kzalloc_node(size, GFP_KERNEL, node);
> + rb = kzalloc_node(struct_size(rb, data_pages, 1), GFP_KERNEL, node);
> if (!rb)
> goto fail;
>
> + rb->nr_pages = nr_pages;
I don't think this is correct.
There is already a logic in place about it a few lines below:
all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
if (!all_buf)
goto fail_all_buf;
rb->user_page = all_buf;
rb->data_pages[0] = all_buf + PAGE_SIZE;
if (nr_pages) { <--- here
rb->nr_pages = 1; <---
rb->page_order = ilog2(nr_pages);
}
I think that what is needed is to move this block just 2 lines above,
(before rb->data_pages[0] = ...)
I'm also wondering what should be done if nr_pages = 0.
CJ
> INIT_WORK(&rb->work, rb_free_work);
>
> all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
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