[PATCH v3 08/10] refcount: Consolidate implementations of refcount_t
From: Will Deacon
Date: Mon Oct 07 2019 - 11:47:35 EST
The generic implementation of refcount_t should be good enough for
everybody, so remove ARCH_HAS_REFCOUNT and REFCOUNT_FULL entirely,
leaving the generic implementation enabled unconditionally.
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Elena Reshetova <elena.reshetova@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
---
arch/Kconfig | 21 -----
arch/arm/Kconfig | 1 -
arch/arm64/Kconfig | 1 -
arch/s390/configs/debug_defconfig | 1 -
arch/x86/Kconfig | 1 -
arch/x86/include/asm/asm.h | 6 --
arch/x86/include/asm/refcount.h | 126 -----------------------------
arch/x86/mm/extable.c | 49 -----------
drivers/gpu/drm/i915/Kconfig.debug | 1 -
include/linux/refcount.h | 122 +++++++++-------------------
lib/refcount.c | 2 +-
11 files changed, 41 insertions(+), 290 deletions(-)
delete mode 100644 arch/x86/include/asm/refcount.h
diff --git a/arch/Kconfig b/arch/Kconfig
index 5f8a5d84dbbe..8bcc1c746142 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -892,27 +892,6 @@ config STRICT_MODULE_RWX
config ARCH_HAS_PHYS_TO_DMA
bool
-config ARCH_HAS_REFCOUNT
- bool
- help
- An architecture selects this when it has implemented refcount_t
- using open coded assembly primitives that provide an optimized
- refcount_t implementation, possibly at the expense of some full
- refcount state checks of CONFIG_REFCOUNT_FULL=y.
-
- The refcount overflow check behavior, however, must be retained.
- Catching overflows is the primary security concern for protecting
- against bugs in reference counts.
-
-config REFCOUNT_FULL
- bool "Perform full reference count validation at the expense of speed"
- help
- Enabling this switches the refcounting infrastructure from a fast
- unchecked atomic_t implementation to a fully state checked
- implementation, which can be (slightly) slower but provides protections
- against various use-after-free conditions that can be used in
- security flaw exploits.
-
config HAVE_ARCH_COMPILER_H
bool
help
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 8a50efb559f3..0d3c5d7cceb7 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -117,7 +117,6 @@ config ARM
select OLD_SIGSUSPEND3
select PCI_SYSCALL if PCI
select PERF_USE_VMALLOC
- select REFCOUNT_FULL
select RTC_LIB
select SYS_SUPPORTS_APM_EMULATION
# Above selects are sorted alphabetically; please add new ones
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 41a9b4257b72..bc990d3abfe9 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -181,7 +181,6 @@ config ARM64
select PCI_SYSCALL if PCI
select POWER_RESET
select POWER_SUPPLY
- select REFCOUNT_FULL
select SPARSE_IRQ
select SWIOTLB
select SYSCTL_EXCEPTION_TRACE
diff --git a/arch/s390/configs/debug_defconfig b/arch/s390/configs/debug_defconfig
index 347f48702edb..ded15e2add36 100644
--- a/arch/s390/configs/debug_defconfig
+++ b/arch/s390/configs/debug_defconfig
@@ -61,7 +61,6 @@ CONFIG_OPROFILE=m
CONFIG_KPROBES=y
CONFIG_JUMP_LABEL=y
CONFIG_STATIC_KEYS_SELFTEST=y
-CONFIG_REFCOUNT_FULL=y
CONFIG_LOCK_EVENT_COUNTS=y
CONFIG_MODULES=y
CONFIG_MODULE_FORCE_LOAD=y
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index d6e1faa28c58..fa6274f1e370 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -73,7 +73,6 @@ config X86
select ARCH_HAS_PMEM_API if X86_64
select ARCH_HAS_PTE_DEVMAP if X86_64
select ARCH_HAS_PTE_SPECIAL
- select ARCH_HAS_REFCOUNT
select ARCH_HAS_UACCESS_FLUSHCACHE if X86_64
select ARCH_HAS_UACCESS_MCSAFE if X86_64 && X86_MCE
select ARCH_HAS_SET_MEMORY
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 3ff577c0b102..5a0c14ebef70 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -139,9 +139,6 @@
# define _ASM_EXTABLE_EX(from, to) \
_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
-# define _ASM_EXTABLE_REFCOUNT(from, to) \
- _ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
-
# define _ASM_NOKPROBE(entry) \
.pushsection "_kprobe_blacklist","aw" ; \
_ASM_ALIGN ; \
@@ -170,9 +167,6 @@
# define _ASM_EXTABLE_EX(from, to) \
_ASM_EXTABLE_HANDLE(from, to, ex_handler_ext)
-# define _ASM_EXTABLE_REFCOUNT(from, to) \
- _ASM_EXTABLE_HANDLE(from, to, ex_handler_refcount)
-
/* For C file, we already have NOKPROBE_SYMBOL macro */
#endif
diff --git a/arch/x86/include/asm/refcount.h b/arch/x86/include/asm/refcount.h
deleted file mode 100644
index 232f856e0db0..000000000000
--- a/arch/x86/include/asm/refcount.h
+++ /dev/null
@@ -1,126 +0,0 @@
-#ifndef __ASM_X86_REFCOUNT_H
-#define __ASM_X86_REFCOUNT_H
-/*
- * x86-specific implementation of refcount_t. Based on PAX_REFCOUNT from
- * PaX/grsecurity.
- */
-#include <linux/refcount.h>
-#include <asm/bug.h>
-
-/*
- * This is the first portion of the refcount error handling, which lives in
- * .text.unlikely, and is jumped to from the CPU flag check (in the
- * following macros). This saves the refcount value location into CX for
- * the exception handler to use (in mm/extable.c), and then triggers the
- * central refcount exception. The fixup address for the exception points
- * back to the regular execution flow in .text.
- */
-#define _REFCOUNT_EXCEPTION \
- ".pushsection .text..refcount\n" \
- "111:\tlea %[var], %%" _ASM_CX "\n" \
- "112:\t" ASM_UD2 "\n" \
- ASM_UNREACHABLE \
- ".popsection\n" \
- "113:\n" \
- _ASM_EXTABLE_REFCOUNT(112b, 113b)
-
-/* Trigger refcount exception if refcount result is negative. */
-#define REFCOUNT_CHECK_LT_ZERO \
- "js 111f\n\t" \
- _REFCOUNT_EXCEPTION
-
-/* Trigger refcount exception if refcount result is zero or negative. */
-#define REFCOUNT_CHECK_LE_ZERO \
- "jz 111f\n\t" \
- REFCOUNT_CHECK_LT_ZERO
-
-/* Trigger refcount exception unconditionally. */
-#define REFCOUNT_ERROR \
- "jmp 111f\n\t" \
- _REFCOUNT_EXCEPTION
-
-static __always_inline void refcount_add(unsigned int i, refcount_t *r)
-{
- asm volatile(LOCK_PREFIX "addl %1,%0\n\t"
- REFCOUNT_CHECK_LT_ZERO
- : [var] "+m" (r->refs.counter)
- : "ir" (i)
- : "cc", "cx");
-}
-
-static __always_inline void refcount_inc(refcount_t *r)
-{
- asm volatile(LOCK_PREFIX "incl %0\n\t"
- REFCOUNT_CHECK_LT_ZERO
- : [var] "+m" (r->refs.counter)
- : : "cc", "cx");
-}
-
-static __always_inline void refcount_dec(refcount_t *r)
-{
- asm volatile(LOCK_PREFIX "decl %0\n\t"
- REFCOUNT_CHECK_LE_ZERO
- : [var] "+m" (r->refs.counter)
- : : "cc", "cx");
-}
-
-static __always_inline __must_check
-bool refcount_sub_and_test(unsigned int i, refcount_t *r)
-{
- bool ret = GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl",
- REFCOUNT_CHECK_LT_ZERO,
- r->refs.counter, e, "er", i, "cx");
-
- if (ret) {
- smp_acquire__after_ctrl_dep();
- return true;
- }
-
- return false;
-}
-
-static __always_inline __must_check bool refcount_dec_and_test(refcount_t *r)
-{
- bool ret = GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl",
- REFCOUNT_CHECK_LT_ZERO,
- r->refs.counter, e, "cx");
-
- if (ret) {
- smp_acquire__after_ctrl_dep();
- return true;
- }
-
- return false;
-}
-
-static __always_inline __must_check
-bool refcount_add_not_zero(unsigned int i, refcount_t *r)
-{
- int c, result;
-
- c = atomic_read(&(r->refs));
- do {
- if (unlikely(c == 0))
- return false;
-
- result = c + i;
-
- /* Did we try to increment from/to an undesirable state? */
- if (unlikely(c < 0 || c == INT_MAX || result < c)) {
- asm volatile(REFCOUNT_ERROR
- : : [var] "m" (r->refs.counter)
- : "cc", "cx");
- break;
- }
-
- } while (!atomic_try_cmpxchg(&(r->refs), &c, result));
-
- return c != 0;
-}
-
-static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r)
-{
- return refcount_add_not_zero(1, r);
-}
-
-#endif
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 4d75bc656f97..30bb0bd3b1b8 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -44,55 +44,6 @@ __visible bool ex_handler_fault(const struct exception_table_entry *fixup,
}
EXPORT_SYMBOL_GPL(ex_handler_fault);
-/*
- * Handler for UD0 exception following a failed test against the
- * result of a refcount inc/dec/add/sub.
- */
-__visible bool ex_handler_refcount(const struct exception_table_entry *fixup,
- struct pt_regs *regs, int trapnr,
- unsigned long error_code,
- unsigned long fault_addr)
-{
- /* First unconditionally saturate the refcount. */
- *(int *)regs->cx = INT_MIN / 2;
-
- /*
- * Strictly speaking, this reports the fixup destination, not
- * the fault location, and not the actually overflowing
- * instruction, which is the instruction before the "js", but
- * since that instruction could be a variety of lengths, just
- * report the location after the overflow, which should be close
- * enough for finding the overflow, as it's at least back in
- * the function, having returned from .text.unlikely.
- */
- regs->ip = ex_fixup_addr(fixup);
-
- /*
- * This function has been called because either a negative refcount
- * value was seen by any of the refcount functions, or a zero
- * refcount value was seen by refcount_dec().
- *
- * If we crossed from INT_MAX to INT_MIN, OF (Overflow Flag: result
- * wrapped around) will be set. Additionally, seeing the refcount
- * reach 0 will set ZF (Zero Flag: result was zero). In each of
- * these cases we want a report, since it's a boundary condition.
- * The SF case is not reported since it indicates post-boundary
- * manipulations below zero or above INT_MAX. And if none of the
- * flags are set, something has gone very wrong, so report it.
- */
- if (regs->flags & (X86_EFLAGS_OF | X86_EFLAGS_ZF)) {
- bool zero = regs->flags & X86_EFLAGS_ZF;
-
- refcount_error_report(regs, zero ? "hit zero" : "overflow");
- } else if ((regs->flags & X86_EFLAGS_SF) == 0) {
- /* Report if none of OF, ZF, nor SF are set. */
- refcount_error_report(regs, "unexpected saturation");
- }
-
- return true;
-}
-EXPORT_SYMBOL(ex_handler_refcount);
-
/*
* Handler for when we fail to restore a task's FPU state. We should never get
* here because the FPU state of a task using the FPU (task->thread.fpu.state)
diff --git a/drivers/gpu/drm/i915/Kconfig.debug b/drivers/gpu/drm/i915/Kconfig.debug
index 00786a142ff0..1400fce39c58 100644
--- a/drivers/gpu/drm/i915/Kconfig.debug
+++ b/drivers/gpu/drm/i915/Kconfig.debug
@@ -22,7 +22,6 @@ config DRM_I915_DEBUG
depends on DRM_I915
select DEBUG_FS
select PREEMPT_COUNT
- select REFCOUNT_FULL
select I2C_CHARDEV
select STACKDEPOT
select DRM_DP_AUX_CHARDEV
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index e148639a9224..662ccb81dd65 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -1,8 +1,48 @@
/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Variant of atomic_t specialized for reference counts.
+ *
+ * The interface matches the atomic_t interface (to aid in porting) but only
+ * provides the few functions one should use for reference counting.
+ *
+ * It differs in that the counter saturates at REFCOUNT_SATURATED and will not
+ * move once there. This avoids wrapping the counter and causing 'spurious'
+ * use-after-free issues.
+ *
+ * Memory ordering rules are slightly relaxed wrt regular atomic_t functions
+ * and provide only what is strictly required for refcounts.
+ *
+ * The increments are fully relaxed; these will not provide ordering. The
+ * rationale is that whatever is used to obtain the object we're increasing the
+ * reference count on will provide the ordering. For locked data structures,
+ * its the lock acquire, for RCU/lockless data structures its the dependent
+ * load.
+ *
+ * Do note that inc_not_zero() provides a control dependency which will order
+ * future stores against the inc, this ensures we'll never modify the object
+ * if we did not in fact acquire a reference.
+ *
+ * The decrements will provide release order, such that all the prior loads and
+ * stores will be issued before, it also provides a control dependency, which
+ * will order us against the subsequent free().
+ *
+ * The control dependency is against the load of the cmpxchg (ll/sc) that
+ * succeeded. This means the stores aren't fully ordered, but this is fine
+ * because the 1->0 transition indicates no concurrency.
+ *
+ * Note that the allocator is responsible for ordering things between free()
+ * and alloc().
+ *
+ * The decrements dec_and_test() and sub_and_test() also provide acquire
+ * ordering on success.
+ *
+ */
+
#ifndef _LINUX_REFCOUNT_H
#define _LINUX_REFCOUNT_H
#include <linux/atomic.h>
+#include <linux/bug.h>
#include <linux/compiler.h>
#include <linux/limits.h>
#include <linux/spinlock_types.h>
@@ -56,48 +96,6 @@ static inline unsigned int refcount_read(const refcount_t *r)
return atomic_read(&r->refs);
}
-#ifdef CONFIG_REFCOUNT_FULL
-#include <linux/bug.h>
-
-/*
- * Variant of atomic_t specialized for reference counts.
- *
- * The interface matches the atomic_t interface (to aid in porting) but only
- * provides the few functions one should use for reference counting.
- *
- * It differs in that the counter saturates at REFCOUNT_SATURATED and will not
- * move once there. This avoids wrapping the counter and causing 'spurious'
- * use-after-free issues.
- *
- * Memory ordering rules are slightly relaxed wrt regular atomic_t functions
- * and provide only what is strictly required for refcounts.
- *
- * The increments are fully relaxed; these will not provide ordering. The
- * rationale is that whatever is used to obtain the object we're increasing the
- * reference count on will provide the ordering. For locked data structures,
- * its the lock acquire, for RCU/lockless data structures its the dependent
- * load.
- *
- * Do note that inc_not_zero() provides a control dependency which will order
- * future stores against the inc, this ensures we'll never modify the object
- * if we did not in fact acquire a reference.
- *
- * The decrements will provide release order, such that all the prior loads and
- * stores will be issued before, it also provides a control dependency, which
- * will order us against the subsequent free().
- *
- * The control dependency is against the load of the cmpxchg (ll/sc) that
- * succeeded. This means the stores aren't fully ordered, but this is fine
- * because the 1->0 transition indicates no concurrency.
- *
- * Note that the allocator is responsible for ordering things between free()
- * and alloc().
- *
- * The decrements dec_and_test() and sub_and_test() also provide acquire
- * ordering on success.
- *
- */
-
/**
* refcount_add_not_zero - add a value to a refcount unless it is 0
* @i: the value to add to the refcount
@@ -260,46 +258,6 @@ static inline void refcount_dec(refcount_t *r)
if (unlikely(atomic_fetch_sub_release(1, &r->refs) <= 1))
refcount_warn_saturate(r, REFCOUNT_DEC_LEAK);
}
-#else /* CONFIG_REFCOUNT_FULL */
-# ifdef CONFIG_ARCH_HAS_REFCOUNT
-# include <asm/refcount.h>
-# else
-static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)
-{
- return atomic_add_unless(&r->refs, i, 0);
-}
-
-static inline void refcount_add(int i, refcount_t *r)
-{
- atomic_add(i, &r->refs);
-}
-
-static inline __must_check bool refcount_inc_not_zero(refcount_t *r)
-{
- return atomic_add_unless(&r->refs, 1, 0);
-}
-
-static inline void refcount_inc(refcount_t *r)
-{
- atomic_inc(&r->refs);
-}
-
-static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r)
-{
- return atomic_sub_and_test(i, &r->refs);
-}
-
-static inline __must_check bool refcount_dec_and_test(refcount_t *r)
-{
- return atomic_dec_and_test(&r->refs);
-}
-
-static inline void refcount_dec(refcount_t *r)
-{
- atomic_dec(&r->refs);
-}
-# endif /* !CONFIG_ARCH_HAS_REFCOUNT */
-#endif /* !CONFIG_REFCOUNT_FULL */
extern __must_check bool refcount_dec_if_one(refcount_t *r);
extern __must_check bool refcount_dec_not_one(refcount_t *r);
diff --git a/lib/refcount.c b/lib/refcount.c
index 6a61d39f9390..4ba991c2335c 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -1,6 +1,6 @@
// SPDX-License-Identifier: GPL-2.0
/*
- * Out-of-line refcount functions common to all refcount implementations.
+ * Out-of-line refcount functions.
*/
#include <linux/mutex.h>
--
2.23.0.581.g78d2f28ef7-goog