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locking/refcount: Move saturation warnings out of line 

Having the refcount saturation and warnings inline bloats the text,
despite the fact that these paths should never be executed in normal
operation.

Move the refcount saturation and warnings out of line to reduce the
image size when refcount_t checking is enabled. Relative to an x86_64
defconfig, the sizes reported by bloat-o-meter are:

 # defconfig+REFCOUNT_FULL, inline saturation (i.e. before this patch)
 Total: Before=14762076, After=14915442, chg +1.04%

 # defconfig+REFCOUNT_FULL, out-of-line saturation (i.e. after this patch)
 Total: Before=14762076, After=14835497, chg +0.50%

A side-effect of this change is that we now only get one warning per
refcount saturation type, rather than one per problematic call-site.

Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Hanjun Guo <guohanjun@huawei.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Elena Reshetova <elena.reshetova@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191121115902.2551-7-will@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Will Deacon 2019-11-21 11:58:58 +00:00 committed by Ingo Molnar
parent dcb786493f
commit 1eb085d942
2 changed files with 48 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

39
include/linux/refcount.h
View File

@ -23,6 +23,16 @@ typedef struct refcount_struct {
#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), } #define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
enum refcount_saturation_type {
REFCOUNT_ADD_NOT_ZERO_OVF,
REFCOUNT_ADD_OVF,
REFCOUNT_ADD_UAF,
REFCOUNT_SUB_UAF,
REFCOUNT_DEC_LEAK,
};
void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t);
/** /**
* refcount_set - set a refcount's value * refcount_set - set a refcount's value
* @r: the refcount * @r: the refcount
@ -154,10 +164,8 @@ static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)
break; break;
} while (!atomic_try_cmpxchg_relaxed(&r->refs, &old, old + i)); } while (!atomic_try_cmpxchg_relaxed(&r->refs, &old, old + i));
if (unlikely(old < 0 || old + i < 0)) { if (unlikely(old < 0 || old + i < 0))
refcount_set(r, REFCOUNT_SATURATED); refcount_warn_saturate(r, REFCOUNT_ADD_NOT_ZERO_OVF);
WARN_ONCE(1, "refcount_t: saturated; leaking memory.\n");
}
return old; return old;
} }
@ -182,11 +190,10 @@ static inline void refcount_add(int i, refcount_t *r)
{ {
int old = atomic_fetch_add_relaxed(i, &r->refs); int old = atomic_fetch_add_relaxed(i, &r->refs);
WARN_ONCE(!old, "refcount_t: addition on 0; use-after-free.\n"); if (unlikely(!old))
if (unlikely(old <= 0 || old + i <= 0)) { refcount_warn_saturate(r, REFCOUNT_ADD_UAF);
refcount_set(r, REFCOUNT_SATURATED); else if (unlikely(old < 0 || old + i < 0))
WARN_ONCE(old, "refcount_t: saturated; leaking memory.\n"); refcount_warn_saturate(r, REFCOUNT_ADD_OVF);
}
} }
/** /**
@ -253,10 +260,8 @@ static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r)
return true; return true;
} }
if (unlikely(old < 0 || old - i < 0)) { if (unlikely(old < 0 || old - i < 0))
refcount_set(r, REFCOUNT_SATURATED); refcount_warn_saturate(r, REFCOUNT_SUB_UAF);
WARN_ONCE(1, "refcount_t: underflow; use-after-free.\n");
}
return false; return false;
} }
@ -291,12 +296,8 @@ static inline __must_check bool refcount_dec_and_test(refcount_t *r)
*/ */
static inline void refcount_dec(refcount_t *r) static inline void refcount_dec(refcount_t *r)
{ {
int old = atomic_fetch_sub_release(1, &r->refs); if (unlikely(atomic_fetch_sub_release(1, &r->refs) <= 1))
refcount_warn_saturate(r, REFCOUNT_DEC_LEAK);
if (unlikely(old <= 1)) {
refcount_set(r, REFCOUNT_SATURATED);
WARN_ONCE(1, "refcount_t: decrement hit 0; leaking memory.\n");
}
} }
#else /* CONFIG_REFCOUNT_FULL */ #else /* CONFIG_REFCOUNT_FULL */

28
lib/refcount.c
View File

@ -8,6 +8,34 @@
#include <linux/spinlock.h> #include <linux/spinlock.h>
#include <linux/bug.h> #include <linux/bug.h>
#define REFCOUNT_WARN(str) WARN_ONCE(1, "refcount_t: " str ".\n")
void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
{
refcount_set(r, REFCOUNT_SATURATED);
switch (t) {
case REFCOUNT_ADD_NOT_ZERO_OVF:
REFCOUNT_WARN("saturated; leaking memory");
break;
case REFCOUNT_ADD_OVF:
REFCOUNT_WARN("saturated; leaking memory");
break;
case REFCOUNT_ADD_UAF:
REFCOUNT_WARN("addition on 0; use-after-free");
break;
case REFCOUNT_SUB_UAF:
REFCOUNT_WARN("underflow; use-after-free");
break;
case REFCOUNT_DEC_LEAK:
REFCOUNT_WARN("decrement hit 0; leaking memory");
break;
default:
REFCOUNT_WARN("unknown saturation event!?");
}
}
EXPORT_SYMBOL(refcount_warn_saturate);
/** /**
* refcount_dec_if_one - decrement a refcount if it is 1 * refcount_dec_if_one - decrement a refcount if it is 1
* @r: the refcount * @r: the refcount