Re: [PATCH 1/2] perf/core: Bail out early if the request AUX area is out of bound

From: James Clark
Date: Mon Jun 12 2023 - 04:47:34 EST

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On 12/06/2023 08:38, Leo Yan wrote:
> Hi Shuai,
>
> On Mon, Jun 12, 2023 at 01:24:51PM +0800, Shuai Xue wrote:
>> When perf-record with a large AUX area, e.g 4GB, it fails with:
>>
>> #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1
>> failed to mmap with 12 (Cannot allocate memory)
>>
>> and it reveals a WARNING with __alloc_pages:
>>
>> [ 66.595604] ------------[ cut here ]------------
>> [ 66.600206] WARNING: CPU: 44 PID: 17573 at mm/page_alloc.c:5568 __alloc_pages+0x1ec/0x248
>> [ 66.608375] Modules linked in: ip6table_filter(E) ip6_tables(E) iptable_filter(E) ebtable_nat(E) ebtables(E) aes_ce_blk(E) vfat(E) fat(E) aes_ce_cipher(E) crct10dif_ce(E) ghash_ce(E) sm4_ce_cipher(E) sm4(E) sha2_ce(E) sha256_arm64(E) sha1_ce(E) acpi_ipmi(E) sbsa_gwdt(E) sg(E) ipmi_si(E) ipmi_devintf(E) ipmi_msghandler(E) ip_tables(E) sd_mod(E) ast(E) drm_kms_helper(E) syscopyarea(E) sysfillrect(E) nvme(E) sysimgblt(E) i2c_algo_bit(E) nvme_core(E) drm_shmem_helper(E) ahci(E) t10_pi(E) libahci(E) drm(E) crc64_rocksoft(E) i40e(E) crc64(E) libata(E) i2c_core(E)
>> [ 66.657719] CPU: 44 PID: 17573 Comm: perf Kdump: loaded Tainted: G E 6.3.0-rc4+ #58
>> [ 66.666749] Hardware name: Default Default/Default, BIOS 1.2.M1.AL.P.139.00 03/22/2023
>> [ 66.674650] pstate: 23400009 (nzCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
>> [ 66.681597] pc : __alloc_pages+0x1ec/0x248
>> [ 66.685680] lr : __kmalloc_large_node+0xc0/0x1f8
>> [ 66.690285] sp : ffff800020523980
>> [ 66.693585] pmr_save: 000000e0
>> [ 66.696624] x29: ffff800020523980 x28: ffff000832975800 x27: 0000000000000000
>> [ 66.703746] x26: 0000000000100000 x25: 0000000000100000 x24: ffff8000083615d0
>> [ 66.710866] x23: 0000000000040dc0 x22: ffff000823d6d140 x21: 000000000000000b
>> [ 66.717987] x20: 000000000000000b x19: 0000000000000000 x18: 0000000000000030
>> [ 66.725108] x17: 0000000000000000 x16: ffff800008f05be8 x15: ffff000823d6d6d0
>> [ 66.732229] x14: 0000000000000000 x13: 343373656761705f x12: 726e202c30206574
>> [ 66.739350] x11: 00000000ffff7fff x10: 00000000ffff7fff x9 : ffff8000083af570
>> [ 66.746471] x8 : 00000000000bffe8 x7 : c0000000ffff7fff x6 : 000000000005fff4
>> [ 66.753592] x5 : 0000000000000000 x4 : ffff000823d6d8d8 x3 : 0000000000000000
>> [ 66.760713] x2 : 0000000000000000 x1 : 0000000000000001 x0 : 0000000000040dc0
>> [ 66.767834] Call trace:
>> [ 66.770267] __alloc_pages+0x1ec/0x248
>> [ 66.774003] __kmalloc_large_node+0xc0/0x1f8
>> [ 66.778259] __kmalloc_node+0x134/0x1e8
>> [ 66.782081] rb_alloc_aux+0xe0/0x298
>> [ 66.785643] perf_mmap+0x440/0x660
>> [ 66.789031] mmap_region+0x308/0x8a8
>> [ 66.792593] do_mmap+0x3c0/0x528
>> [ 66.795807] vm_mmap_pgoff+0xf4/0x1b8
>> [ 66.799456] ksys_mmap_pgoff+0x18c/0x218
>> [ 66.803365] __arm64_sys_mmap+0x38/0x58
>> [ 66.807187] invoke_syscall+0x50/0x128
>> [ 66.810922] el0_svc_common.constprop.0+0x58/0x188
>> [ 66.815698] do_el0_svc+0x34/0x50
>> [ 66.818999] el0_svc+0x34/0x108
>> [ 66.822127] el0t_64_sync_handler+0xb8/0xc0
>> [ 66.826296] el0t_64_sync+0x1a4/0x1a8
>> [ 66.829946] ---[ end trace 0000000000000000 ]---
>>
>> The pages for AUX area are organized as rb->aux_pages[] which alloced by
>> kcalloc_node() later. The kcalloc() family guarantees the pages are
>> physically contiguous (and virtually contiguous) with an order of
>> MAX_ORDER - 1 at maximum.
>
> This description is incorrect. We need to distinguish two things:
>
> AUX trace pages and 'rb->aux_pages' is pointer array which is used to
> maintains these page. Here, the kernel oops reports the error is not
> for AUX trace pages but for failing to allocate the pointer array from
> slab (or slub) area.
>
> Furthermore, I believe the AUX trace pages are only mapped for VMA
> (continuous virtual address), the kernel will defer to map to physical
> pages (which means it's not necessarily continuous physical pages)
> when handling data abort caused by accessing the pages.
>
> When you specify the AUX buffer size to 4GiB, the kernel will convert it
> to page numbers (page size is 4KiB, page number is = 4GiB / 4KiB = 1MiB).
> Since aarch64's pointer type's length is 8 bytes, thus we need to
> allocate the 8MiB buffer from slab/slub, unfortunately, 8MiB crosses the
> limitation set by MAX_ORDER (4KiB ^ (MAX_ORDER - 1) = 4MiB), this is
> why we receive the oops from __alloc_pages().
>
>> So bail out early with -EINVAL if the request AUX area is out of bound,
>> e.g.:
>>
>> #perf record -C 0 -m ,4G -e arm_spe_0// -- sleep 1
>> failed to mmap with 22 (Invalid argument)
>>
>> Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
>> ---
>> kernel/events/core.c | 10 ++++++++++
>> tools/perf/Documentation/perf-record.txt | 3 ++-
>> 2 files changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 435815d..83d4e29 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -6404,6 +6404,16 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
>> return -EINVAL;
>>
>> nr_pages = vma_size / PAGE_SIZE;
>> + /*
>> + * The pages for AUX area are organized as rb->aux_pages[]
>> + * which alloced by kcalloc_node() later. The kcalloc() family
>> + * guarantees the pages are physically contiguous (and
>> + * virtually contiguous) with an order of MAX_ORDER - 1 at
>> + * maximum MAX_ORDER. So bail out early if the request AUX area
>> + * is out of bound.
>> + */
>> + if (get_order(nr_pages * sizeof(void *)) >= MAX_ORDER)
>> + return -EINVAL;
>
> From my view, now kernel has handled this case (I agree it might be
> not directive for outputting error or warning info rather than oops).
>
> If we really want this checking, I'd like to add it in rb_alloc_aux(),
> since rb_alloc_aux() is the place for allocation the memory, thus it's
> right place for the checking memory limitation. And you might need to
> consider the update the comments to avoid confusion.
>
> I am not the best person for the decision, I'd like to leave it to perf
> maintainers and wait for their thoughts.
>
> Thanks,
> Leo

If we were to keep it in the end, it should technically have a
multiplication overflow check on it as well.

James

>
>> mutex_lock(&event->mmap_mutex);
>> ret = -EINVAL;
>> diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
>> index ff815c2..a50a426 100644
>> --- a/tools/perf/Documentation/perf-record.txt
>> +++ b/tools/perf/Documentation/perf-record.txt
>> @@ -236,7 +236,8 @@ OPTIONS
>> specification with appended unit character - B/K/M/G. The
>> size is rounded up to have nearest pages power of two value.
>> Also, by adding a comma, the number of mmap pages for AUX
>> - area tracing can be specified.
>> + area tracing can be specified. With MAX_ORDER set as 11, the
>> + maximum AUX area is limit to 2GB.
>>
>> -g::
>> Enables call-graph (stack chain/backtrace) recording for both
>> --
>> 1.8.3.1
>>

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