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Wed, 26 Nov 2025 11:33:33 -0800 (PST) X-Google-Smtp-Source: AGHT+IG47tmkWhcWx7LLIvtKQsizLgK/XycnA3H/j9qIrssDiOnhoTF9BGJBcCZ0+sksNIxvtyVvrA== X-Received: by 2002:a17:90b:38c7:b0:340:ec6f:5ac5 with SMTP id 98e67ed59e1d1-34733e55021mr16182627a91.2.1764185612922; Wed, 26 Nov 2025 11:33:32 -0800 (PST) Received: from [192.168.192.85] ([50.47.129.42]) by smtp.googlemail.com with ESMTPSA id 98e67ed59e1d1-3476a7bd7f3sm3338986a91.13.2025.11.26.11.33.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 26 Nov 2025 11:33:32 -0800 (PST) Message-ID: Date: Wed, 26 Nov 2025 11:33:31 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] apparmor unaligned memory fixes To: Helge Deller , david laight Cc: Helge Deller , John Paul Adrian Glaubitz , linux-kernel@vger.kernel.org, apparmor@lists.ubuntu.com, linux-security-module@vger.kernel.org, linux-parisc@vger.kernel.org References: <90513f85cc8d060ebccd3972cc7709e4b6f13f34.camel@physik.fu-berlin.de> <20251126104444.29002552@pumpkin> <4034ad19-8e09-440c-a042-a66a488c048b@gmx.de> <20251126142201.27e23076@pumpkin> Content-Language: en-US From: John Johansen Autocrypt: addr=john.johansen@canonical.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/26/25 07:12, Helge Deller wrote: > * david laight : >> On Wed, 26 Nov 2025 12:03:03 +0100 >> Helge Deller wrote: >> >>> On 11/26/25 11:44, david laight wrote: >> ... >>>>> diff --git a/security/apparmor/match.c b/security/apparmor/match.c >>>>> index 26e82ba879d44..3dcc342337aca 100644 >>>>> --- a/security/apparmor/match.c >>>>> +++ b/security/apparmor/match.c >>>>> @@ -71,10 +71,10 @@ static struct table_header *unpack_table(char *blob, size_t bsize) >>>>> u8, u8, byte_to_byte); >>>> >>>> Is that that just memcpy() ? >>> >>> No, it's memcpy() only on big-endian machines. >> >> You've misread the quoting... >> The 'data8' case that was only half there is a memcpy(). >> >>> On little-endian machines it converts from big-endian >>> 16/32-bit ints to little-endian 16/32-bit ints. >>> >>> But I see some potential for optimization here: >>> a) on big-endian machines just use memcpy() >> >> true >> >>> b) on little-endian machines use memcpy() to copy from possibly-unaligned >>> memory to then known-to-be-aligned destination. Then use a loop with >>> be32_to_cpu() instead of get_unaligned_xx() as it's faster. >> >> There is a function that does a loop byteswap of a buffer - no reason >> to re-invent it. > > I assumed there must be something, but I did not see it. Which one? > >> But I doubt it is always (if ever) faster to do a copy and then byteswap. >> The loop control and extra memory accesses kill performance. > > Yes, you are probably right. > >> Not that I've seen a fast get_unaligned() - I don't think gcc or clang >> generate optimal code - For LE I think it is something like: >> low = *(addr & ~3); >> high = *((addr + 3) & ~3); >> shift = (addr & 3) * 8; >> value = low << shift | high >> (32 - shift); >> Note that it is only 2 aligned memory reads - even for 64bit. > > Ok, then maybe we should keep it simple like this patch: > > [PATCH v2] apparmor: Optimize table creation from possibly unaligned memory > > Source blob may come from userspace and might be unaligned. > Try to optize the copying process by avoiding unaligned memory accesses. > > Signed-off-by: Helge Deller > > diff --git a/security/apparmor/include/match.h b/security/apparmor/include/match.h > index 1fbe82f5021b..386da2023d50 100644 > --- a/security/apparmor/include/match.h > +++ b/security/apparmor/include/match.h > @@ -104,16 +104,20 @@ struct aa_dfa { > struct table_header *tables[YYTD_ID_TSIZE]; > }; > > -#define byte_to_byte(X) (X) > +#define byte_to_byte(X) (*(X)) > > #define UNPACK_ARRAY(TABLE, BLOB, LEN, TTYPE, BTYPE, NTOHX) \ > do { \ > typeof(LEN) __i; \ > TTYPE *__t = (TTYPE *) TABLE; \ > BTYPE *__b = (BTYPE *) BLOB; \ > - for (__i = 0; __i < LEN; __i++) { \ > - __t[__i] = NTOHX(__b[__i]); \ > - } \ > + BUILD_BUG_ON(sizeof(TTYPE) != sizeof(BTYPE)); \ > + if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN) || sizeof(BTYPE) == 1) \ > + memcpy(__t, __b, (LEN) * sizeof(BTYPE)); \ > + else /* copy & convert convert from big-endian */ \ > + for (__i = 0; __i < LEN; __i++) { \ > + __t[__i] = NTOHX(&__b[__i]); \ > + } \ > } while (0) > > static inline size_t table_size(size_t len, size_t el_size) > diff --git a/security/apparmor/match.c b/security/apparmor/match.c > index c5a91600842a..13e2f6873329 100644 > --- a/security/apparmor/match.c > +++ b/security/apparmor/match.c > @@ -15,6 +15,7 @@ > #include > #include > #include > +#include > > #include "include/lib.h" > #include "include/match.h" > @@ -70,10 +71,10 @@ static struct table_header *unpack_table(char *blob, size_t bsize) > u8, u8, byte_to_byte); > else if (th.td_flags == YYTD_DATA16) > UNPACK_ARRAY(table->td_data, blob, th.td_lolen, > - u16, __be16, be16_to_cpu); > + u16, __be16, get_unaligned_be16); > else if (th.td_flags == YYTD_DATA32) > UNPACK_ARRAY(table->td_data, blob, th.td_lolen, > - u32, __be32, be32_to_cpu); > + u32, __be32, get_unaligned_be32); > else > goto fail; > /* if table was vmalloced make sure the page tables are synced I think we can make one more tweak, in just not using UNPACK_ARRAY at all for the byte case ie. diff --git a/security/apparmor/match.c b/security/apparmor/match.c index 26e82ba879d44..389202560675c 100644 --- a/security/apparmor/match.c +++ b/security/apparmor/match.c @@ -67,8 +67,7 @@ static struct table_header *unpack_table(char *blob, size_t bsize) table->td_flags = th.td_flags; table->td_lolen = th.td_lolen; if (th.td_flags == YYTD_DATA8) - UNPACK_ARRAY(table->td_data, blob, th.td_lolen, - u8, u8, byte_to_byte); + memcp(table->td_data, blob, th.td_lolen); else if (th.td_flags == YYTD_DATA16) UNPACK_ARRAY(table->td_data, blob, th.td_lolen, u16, __be16, be16_to_cpu);