mirror of https://gitee.com/openkylin/linux.git
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>
This commit is contained in:
Al Viro
Guo Ren
parent
67002814cf
commit
51bb38cb78
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@ -253,7 +253,7 @@ do { \
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extern int __get_user_bad(void);
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#define __copy_user(to, from, n) \
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#define ___copy_to_user(to, from, n) \
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do { \
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int w0, w1, w2, w3; \
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asm volatile( \
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@ -288,31 +288,34 @@ do { \
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" subi %0, 4 \n" \
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" br 3b \n" \
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"5: cmpnei %0, 0 \n" /* 1B */ \
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" bf 8f \n" \
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" bf 13f \n" \
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" ldb %3, (%2, 0) \n" \
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"6: stb %3, (%1, 0) \n" \
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" addi %2, 1 \n" \
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" addi %1, 1 \n" \
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" subi %0, 1 \n" \
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" br 5b \n" \
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"7: br 8f \n" \
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"7: subi %0, 4 \n" \
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"8: subi %0, 4 \n" \
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"12: subi %0, 4 \n" \
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" br 13f \n" \
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".section __ex_table, \"a\" \n" \
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".align 2 \n" \
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".long 2b, 7b \n" \
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".long 9b, 7b \n" \
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".long 10b, 7b \n" \
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".long 2b, 13f \n" \
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".long 4b, 13f \n" \
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".long 6b, 13f \n" \
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".long 9b, 12b \n" \
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".long 10b, 8b \n" \
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".long 11b, 7b \n" \
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".long 4b, 7b \n" \
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".long 6b, 7b \n" \
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".previous \n" \
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"8: \n" \
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"13: \n" \
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: "=r"(n), "=r"(to), "=r"(from), "=r"(w0), \
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"=r"(w1), "=r"(w2), "=r"(w3) \
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: "0"(n), "1"(to), "2"(from) \
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: "memory"); \
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} while (0)
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#define __copy_user_zeroing(to, from, n) \
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#define ___copy_from_user(to, from, n) \
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do { \
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int tmp; \
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int nsave; \
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@ -355,22 +358,22 @@ do { \
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" addi %1, 1 \n" \
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" subi %0, 1 \n" \
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" br 5b \n" \
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"8: mov %3, %0 \n" \
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" movi %4, 0 \n" \
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"9: stb %4, (%1, 0) \n" \
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" addi %1, 1 \n" \
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" subi %3, 1 \n" \
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" cmpnei %3, 0 \n" \
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" bt 9b \n" \
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" br 7f \n" \
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"8: stw %3, (%1, 0) \n" \
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" subi %0, 4 \n" \
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" bf 7f \n" \
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"9: subi %0, 8 \n" \
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" bf 7f \n" \
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"13: stw %3, (%1, 8) \n" \
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" subi %0, 12 \n" \
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" bf 7f \n" \
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".section __ex_table, \"a\" \n" \
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".align 2 \n" \
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".long 2b, 8b \n" \
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".long 2b, 7f \n" \
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".long 4b, 7f \n" \
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".long 6b, 7f \n" \
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".long 10b, 8b \n" \
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".long 11b, 8b \n" \
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".long 12b, 8b \n" \
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".long 4b, 8b \n" \
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".long 6b, 8b \n" \
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".long 11b, 9b \n" \
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".long 12b,13b \n" \
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".previous \n" \
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"7: \n" \
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: "=r"(n), "=r"(to), "=r"(from), "=r"(nsave), \
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@ -7,10 +7,7 @@
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unsigned long raw_copy_from_user(void *to, const void *from,
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unsigned long n)
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{
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if (access_ok(from, n))
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__copy_user_zeroing(to, from, n);
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else
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memset(to, 0, n);
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___copy_from_user(to, from, n);
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return n;
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}
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EXPORT_SYMBOL(raw_copy_from_user);
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@ -18,8 +15,7 @@ EXPORT_SYMBOL(raw_copy_from_user);
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unsigned long raw_copy_to_user(void *to, const void *from,
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unsigned long n)
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{
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if (access_ok(to, n))
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__copy_user(to, from, n);
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___copy_to_user(to, from, n);
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return n;
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}
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EXPORT_SYMBOL(raw_copy_to_user);
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