From: Emil Berg <emil.berg@ericsson.com>
To: "Morten Brørup" <mb@smartsharesystems.com>,
"bugzilla@dpdk.org" <bugzilla@dpdk.org>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: RE: [Bug 1035] __rte_raw_cksum() crash with misaligned pointer
Date: Thu, 16 Jun 2022 06:32:22 +0000 [thread overview]
Message-ID: <AM8PR07MB76662377207F563617C1536198AC9@AM8PR07MB7666.eurprd07.prod.outlook.com> (raw)
In-Reply-To: <AM8PR07MB7666C85896EB2300DC51926498AC9@AM8PR07MB7666.eurprd07.prod.outlook.com>
I've been sketching on an efficient solution to this. What about something along the way below? I've run it with the combinations of:
even buf, even len
even buf, odd len
odd buf, even len
odd buf, odd len
and it seems to give the same results as the older version of __rte_raw_cksum, before 21.03. I ran it without optimizations and such to ensure the compiler didn't insert vector instructions and such so the results were comparable.
static inline uint32_t
__rte_raw_cksum_newest(const void *buf, size_t len, uint32_t sum)
{
const uint8_t *end = buf + len;
uint32_t sum_even = 0;
for (const uint8_t *p = buf + 1; p < end; p += 2) {
sum_even += *p;
}
sum += sum_even << 8;
uint32_t sum_odd = 0;
for (const uint8_t *p = buf; p < end; p += 2) {
sum_odd += *p;
}
sum += sum_odd;
return sum;
}
/Emil
-----Original Message-----
From: Emil Berg
Sent: den 16 juni 2022 07:45
To: Morten Brørup <mb@smartsharesystems.com>; bugzilla@dpdk.org
Cc: dev@dpdk.org
Subject: RE: [Bug 1035] __rte_raw_cksum() crash with misaligned pointer
Hi!
We want the B option, i.e. the 6 bytes option. Perhaps adding alignment detection to __rte_raw_cksum() is a good idea.
A minor comment but I think buf & 1 won't work since buf isn't an integral type, but something along that way.
I'm starting to think about an efficient way to do this.
Thank you!
-----Original Message-----
From: Morten Brørup <mb@smartsharesystems.com>
Sent: den 15 juni 2022 16:41
To: Emil Berg <emil.berg@ericsson.com>; bugzilla@dpdk.org
Cc: dev@dpdk.org
Subject: RE: [Bug 1035] __rte_raw_cksum() crash with misaligned pointer
> From: bugzilla@dpdk.org [mailto:bugzilla@dpdk.org]
> Sent: Wednesday, 15 June 2022 09.16
>
> https://protect2.fireeye.com/v1/url?k=31323334-501d5122-313273af-45444
> 5555731-2e92ae6bf759c0c5&q=1&e=b3fc70af-5d37-4ffb-b34d-9a51927f5f6d&u=
> https%3A%2F%2Fbugs.dpdk.org%2Fshow_bug.cgi%3Fid%3D1035
>
> Bug ID: 1035
> Summary: __rte_raw_cksum() crash with misaligned pointer
> Product: DPDK
> Version: 21.11
> Hardware: All
> OS: All
> Status: UNCONFIRMED
> Severity: normal
> Priority: Normal
> Component: ethdev
> Assignee: dev@dpdk.org
> Reporter: emil.berg@ericsson.com
> Target Milestone: ---
>
> See rte_raw_cksum() in rte_ip.h, which is part of the public API. See
> also the subfunction __rte_raw_cksum().
>
> _rte_raw_cksum assumes that the buffer over which the checksum is
> calculated is an even address (divisible by two). See for example this
> stack overflow
> post:
> https://stackoverflow.com/questions/46790550/c-undefined-behavior-
> strict-aliasing-rule-or-incorrect-alignment
>
> The post explains that there is undefined behavior in C11 when
> "conversion between two pointer types produces a result that is
> incorrectly aligned". When the buf argument starts on an odd address
> we thus have undefined behavior, since a pointer is cast from void* to
> uint16_t*.
>
> In most cases (at least on x86) that isn't a problem, but with higher
> optimization levels it may break due to vector instructions. This new
> function seems to be easier to optimize by the compiler, resulting in
> a crash when the buf argument is odd. Please note that the undefined
> behavior is present in earlier versions of dpdk as well.
>
> Now you're probably thinking: "Just align your buffers". The problem
> is that we have a packet buffer which is aligned. The checksum is
> calculated on a subset of that aligned packet buffer, and that
> sometimes lies on odd addresses.
>
> The question remains if this is an issue with dpdk or not.
I can imagine other systems doing what you describe too. So it needs to be addressed.
Off the top of my head, an easy fix would be updating __rte_raw_cksum() like this:
static inline uint32_t
__rte_raw_cksum(const void *buf, size_t len, uint32_t sum) {
if (likely((buf & 1) == 0)) {
/* The buffer is 16 bit aligned. */
Keep the existing, optimized implementation here.
} else {
/* The buffer is not 16 bit aligned. */
Add a new odd-buf tolerant implementation here.
}
}
However, I'm not sure that it covers your scenario!
The checksum is 16 bit wide, so if you calculate the checksum of e.g. 4 bytes of memory starting at offset 1 in a 6 byte packet buffer, the memory block can be treated as either 4 or 6 bytes relative to the data covered by the checksum, i.e.:
A: XX [01 02] [03 04] XX --> cksum = [04 06]
B: [XX 01] [02 03] [04 XX] --> cksum = [06 04]
Which one do you need?
Perhaps an additional function is required to support your use case, and the documentation for rte_raw_cksum() and __rte_raw_cksum() needs to reflect that the buffer must be 16 bit aligned.
Or the rte_raw_cksum() function can be modified to support an odd buffer pointer as outlined above, with documentation added about alignment of the running checksum.
next prev parent reply other threads:[~2022-06-16 10:48 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-15 7:16 bugzilla
2022-06-15 14:40 ` Morten Brørup
2022-06-16 5:44 ` Emil Berg
2022-06-16 6:27 ` Morten Brørup
2022-06-16 6:32 ` Emil Berg [this message]
2022-06-16 6:44 ` Morten Brørup
2022-06-16 13:58 ` Mattias Rönnblom
2022-06-16 14:36 ` Morten Brørup
2022-06-17 7:32 ` Morten Brørup
2022-06-17 8:45 ` [PATCH] net: fix checksum with unaligned buffer Morten Brørup
2022-06-17 9:06 ` Morten Brørup
2022-06-17 12:17 ` Emil Berg
2022-06-20 10:37 ` Emil Berg
2022-06-20 10:57 ` Morten Brørup
2022-06-21 7:16 ` Emil Berg
2022-06-21 8:05 ` Morten Brørup
2022-06-21 8:23 ` Bruce Richardson
2022-06-21 9:35 ` Morten Brørup
2022-06-22 6:26 ` Emil Berg
2022-06-22 9:18 ` Bruce Richardson
2022-06-22 11:26 ` Morten Brørup
2022-06-22 12:25 ` Emil Berg
2022-06-22 14:01 ` Morten Brørup
2022-06-22 14:03 ` Emil Berg
2022-06-23 5:21 ` Emil Berg
2022-06-23 7:01 ` Morten Brørup
2022-06-23 11:39 ` Emil Berg
2022-06-23 12:18 ` Morten Brørup
2022-06-22 13:44 ` [PATCH v2] " Morten Brørup
2022-06-22 13:54 ` [PATCH v3] " Morten Brørup
2022-06-23 12:39 ` [PATCH v4] " Morten Brørup
2022-06-23 12:51 ` Morten Brørup
2022-06-27 7:56 ` Emil Berg
2022-06-27 10:54 ` Morten Brørup
2022-06-27 12:28 ` Mattias Rönnblom
2022-06-27 12:46 ` Emil Berg
2022-06-27 12:50 ` Emil Berg
2022-06-27 13:22 ` Morten Brørup
2022-06-27 17:22 ` Mattias Rönnblom
2022-06-27 20:21 ` Morten Brørup
2022-06-28 6:28 ` Mattias Rönnblom
2022-06-30 16:28 ` Morten Brørup
2022-07-07 15:21 ` Stanisław Kardach
2022-07-07 18:34 ` [PATCH 1/2] app/test: add cksum performance test Mattias Rönnblom
2022-07-07 18:34 ` [PATCH 2/2] net: have checksum routines accept unaligned data Mattias Rönnblom
2022-07-07 21:44 ` Morten Brørup
2022-07-08 12:43 ` Mattias Rönnblom
2022-07-08 12:56 ` [PATCH v2 1/2] app/test: add cksum performance test Mattias Rönnblom
2022-07-08 12:56 ` [PATCH v2 2/2] net: have checksum routines accept unaligned data Mattias Rönnblom
2022-07-08 14:44 ` Ferruh Yigit
2022-07-11 9:53 ` Olivier Matz
2022-07-11 10:53 ` Mattias Rönnblom
2022-07-11 9:47 ` [PATCH v2 1/2] app/test: add cksum performance test Olivier Matz
2022-07-11 10:42 ` Mattias Rönnblom
2022-07-11 11:33 ` Olivier Matz
2022-07-11 12:11 ` [PATCH v3 " Mattias Rönnblom
2022-07-11 12:11 ` [PATCH v3 2/2] net: have checksum routines accept unaligned data Mattias Rönnblom
2022-07-11 13:25 ` Olivier Matz
2022-08-08 9:25 ` Mattias Rönnblom
2022-09-20 12:09 ` Mattias Rönnblom
2022-09-20 16:10 ` Thomas Monjalon
2022-07-11 13:20 ` [PATCH v3 1/2] app/test: add cksum performance test Olivier Matz
2022-07-08 13:02 ` [PATCH 2/2] net: have checksum routines accept unaligned data Morten Brørup
2022-07-08 13:52 ` Mattias Rönnblom
2022-07-08 14:10 ` Bruce Richardson
2022-07-08 14:30 ` Morten Brørup
2022-06-30 17:41 ` [PATCH v4] net: fix checksum with unaligned buffer Stephen Hemminger
2022-06-30 17:45 ` Stephen Hemminger
2022-07-01 4:11 ` Emil Berg
2022-07-01 16:50 ` Morten Brørup
2022-07-01 17:04 ` Stephen Hemminger
2022-07-01 20:46 ` Morten Brørup
2022-06-16 14:09 ` [Bug 1035] __rte_raw_cksum() crash with misaligned pointer Mattias Rönnblom
2022-10-10 10:40 ` bugzilla
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