On Wed, 26 Nov 2025 16:12:23 +0100 Helge Deller <[email protected]> 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? I can't find it either - just some functions to do an in-place swap. (Which aren't usually a good idea) > > > 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. Not sure that reads right. 'Allow for misaligned data from userspace when byteswapping source blob' ? > > 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)) It's a bit of a shame you need something for the above... David > > #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
