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author | 2020-04-07 02:40:11 +0100 | |
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committer | 2020-05-15 00:16:30 +0800 | |
commit | 51bb38cb78363fdad1f89e87357b7bc73e39ba88 (patch) | |
tree | 178c673b3676ff36a68b6b623e6f2fd25d4f2724 /arch | |
parent | csky: Fixup gdbmacros.txt with name sp in thread_struct (diff) | |
download | linux-51bb38cb78363fdad1f89e87357b7bc73e39ba88.tar.gz linux-51bb38cb78363fdad1f89e87357b7bc73e39ba88.tar.bz2 linux-51bb38cb78363fdad1f89e87357b7bc73e39ba88.zip |
csky: Fixup raw_copy_from_user()
If raw_copy_from_user(to, from, N) returns K, callers expect
the first N - K bytes starting at to to have been replaced with
the contents of corresponding area starting at from and the last
K bytes of destination *left* *unmodified*.
What arch/sky/lib/usercopy.c is doing is broken - it can lead to e.g.
data corruption on write(2).
raw_copy_to_user() is inaccurate about return value, which is a bug,
but consequences are less drastic than for raw_copy_from_user().
And just what are those access_ok() doing in there? I mean, look into
linux/uaccess.h; that's where we do that check (as well as zero tail
on failure in the callers that need zeroing).
AFAICS, all of that shouldn't be hard to fix; something like a patch
below might make a useful starting point.
I would suggest moving these macros into usercopy.c (they are never
used anywhere else) and possibly expanding them there; if you leave
them alive, please at least rename __copy_user_zeroing(). Again,
it must not zero anything on failed read.
Said that, I'm not sure we won't be better off simply turning
usercopy.c into usercopy.S - all that is left there is a couple of
functions, each consisting only of inline asm.
Guo Ren reply:
Yes, raw_copy_from_user is wrong, it's no need zeroing code.
unsigned long _copy_from_user(void *to, const void __user *from,
unsigned long n)
{
unsigned long res = n;
might_fault();
if (likely(access_ok(from, n))) {
kasan_check_write(to, n);
res = raw_copy_from_user(to, from, n);
}
if (unlikely(res))
memset(to + (n - res), 0, res);
return res;
}
EXPORT_SYMBOL(_copy_from_user);
You are right and access_ok() should be removed.
but, how about:
do {
...
"2: stw %3, (%1, 0) \n" \
+ " subi %0, 4 \n" \
"9: stw %4, (%1, 4) \n" \
+ " subi %0, 4 \n" \
"10: stw %5, (%1, 8) \n" \
+ " subi %0, 4 \n" \
"11: stw %6, (%1, 12) \n" \
+ " subi %0, 4 \n" \
" addi %2, 16 \n" \
" addi %1, 16 \n" \
Don't expand __ex_table
AI Viro reply:
Hey, I've no idea about the instruction scheduling on csky -
if that doesn't slow the things down, all the better. It's just
that copy_to_user() and friends are on fairly hot codepaths,
and in quite a few situations they will dominate the speed of
e.g. read(2). So I tried to keep the fast path unchanged.
Up to the architecture maintainers, obviously. Which would be
you...
As for the fixups size increase (__ex_table size is unchanged)...
You have each of those macros expanded exactly once.
So the size is not a serious argument, IMO - useless complexity
would be, if it is, in fact, useless; the size... not really,
especially since those extra subi will at least offset it.
Again, up to you - asm optimizations of (essentially)
memcpy()-style loops are tricky and can depend upon the
fairly subtle details of architecture. So even on something
I know reasonably well I would resort to direct experiments
if I can't pass the buck to architecture maintainers.
It *is* worth optimizing - this is where read() from a file
that is already in page cache spends most of the time, etc.
Guo Ren reply:
Thx, after fixup some typo “sub %0, 4”, apply the patch.
TODO:
- user copy/from codes are still need optimizing.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/csky/include/asm/uaccess.h | 49 | ||||
-rw-r--r-- | arch/csky/lib/usercopy.c | 8 |
2 files changed, 28 insertions, 29 deletions
diff --git a/arch/csky/include/asm/uaccess.h b/arch/csky/include/asm/uaccess.h index abefa125b93c..1633ffe5ae15 100644 --- a/arch/csky/include/asm/uaccess.h +++ b/arch/csky/include/asm/uaccess.h @@ -253,7 +253,7 @@ do { \ extern int __get_user_bad(void); -#define __copy_user(to, from, n) \ +#define ___copy_to_user(to, from, n) \ do { \ int w0, w1, w2, w3; \ asm volatile( \ @@ -288,31 +288,34 @@ do { \ " subi %0, 4 \n" \ " br 3b \n" \ "5: cmpnei %0, 0 \n" /* 1B */ \ - " bf 8f \n" \ + " bf 13f \n" \ " ldb %3, (%2, 0) \n" \ "6: stb %3, (%1, 0) \n" \ " addi %2, 1 \n" \ " addi %1, 1 \n" \ " subi %0, 1 \n" \ " br 5b \n" \ - "7: br 8f \n" \ + "7: subi %0, 4 \n" \ + "8: subi %0, 4 \n" \ + "12: subi %0, 4 \n" \ + " br 13f \n" \ ".section __ex_table, \"a\" \n" \ ".align 2 \n" \ - ".long 2b, 7b \n" \ - ".long 9b, 7b \n" \ - ".long 10b, 7b \n" \ + ".long 2b, 13f \n" \ + ".long 4b, 13f \n" \ + ".long 6b, 13f \n" \ + ".long 9b, 12b \n" \ + ".long 10b, 8b \n" \ ".long 11b, 7b \n" \ - ".long 4b, 7b \n" \ - ".long 6b, 7b \n" \ ".previous \n" \ - "8: \n" \ + "13: \n" \ : "=r"(n), "=r"(to), "=r"(from), "=r"(w0), \ "=r"(w1), "=r"(w2), "=r"(w3) \ : "0"(n), "1"(to), "2"(from) \ : "memory"); \ } while (0) -#define __copy_user_zeroing(to, from, n) \ +#define ___copy_from_user(to, from, n) \ do { \ int tmp; \ int nsave; \ @@ -355,22 +358,22 @@ do { \ " addi %1, 1 \n" \ " subi %0, 1 \n" \ " br 5b \n" \ - "8: mov %3, %0 \n" \ - " movi %4, 0 \n" \ - "9: stb %4, (%1, 0) \n" \ - " addi %1, 1 \n" \ - " subi %3, 1 \n" \ - " cmpnei %3, 0 \n" \ - " bt 9b \n" \ - " br 7f \n" \ + "8: stw %3, (%1, 0) \n" \ + " subi %0, 4 \n" \ + " bf 7f \n" \ + "9: subi %0, 8 \n" \ + " bf 7f \n" \ + "13: stw %3, (%1, 8) \n" \ + " subi %0, 12 \n" \ + " bf 7f \n" \ ".section __ex_table, \"a\" \n" \ ".align 2 \n" \ - ".long 2b, 8b \n" \ + ".long 2b, 7f \n" \ + ".long 4b, 7f \n" \ + ".long 6b, 7f \n" \ ".long 10b, 8b \n" \ - ".long 11b, 8b \n" \ - ".long 12b, 8b \n" \ - ".long 4b, 8b \n" \ - ".long 6b, 8b \n" \ + ".long 11b, 9b \n" \ + ".long 12b,13b \n" \ ".previous \n" \ "7: \n" \ : "=r"(n), "=r"(to), "=r"(from), "=r"(nsave), \ diff --git a/arch/csky/lib/usercopy.c b/arch/csky/lib/usercopy.c index 647a23986fb5..3c9bd645e643 100644 --- a/arch/csky/lib/usercopy.c +++ b/arch/csky/lib/usercopy.c @@ -7,10 +7,7 @@ unsigned long raw_copy_from_user(void *to, const void *from, unsigned long n) { - if (access_ok(from, n)) - __copy_user_zeroing(to, from, n); - else - memset(to, 0, n); + ___copy_from_user(to, from, n); return n; } EXPORT_SYMBOL(raw_copy_from_user); @@ -18,8 +15,7 @@ EXPORT_SYMBOL(raw_copy_from_user); unsigned long raw_copy_to_user(void *to, const void *from, unsigned long n) { - if (access_ok(to, n)) - __copy_user(to, from, n); + ___copy_to_user(to, from, n); return n; } EXPORT_SYMBOL(raw_copy_to_user); |