On 11/26/25 07:12, Helge Deller wrote:
* david laight <[email protected]>:
On Wed, 26 Nov 2025 12:03:03 +0100
Helge Deller <[email protected]> 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 <[email protected]>
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 <linux/vmalloc.h>
#include <linux/err.h>
#include <linux/kref.h>
+#include <linux/unaligned.h>
#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);
