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locking/refcount: Consolidate implementations of refcount_t

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.

Signed-off-by: Will Deacon <will@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Acked-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/20191121115902.2551-9-will@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
master
Will Deacon 2 years ago
committed by Ingo Molnar
parent
commit
fb041bb7c0
11 changed files with 59 additions and 308 deletions
  1. +0
    -21
      arch/Kconfig
  2. +0
    -1
      arch/arm/Kconfig
  3. +0
    -1
      arch/arm64/Kconfig
  4. +0
    -1
      arch/s390/configs/debug_defconfig
  5. +0
    -1
      arch/x86/Kconfig
  6. +0
    -6
      arch/x86/include/asm/asm.h
  7. +0
    -126
      arch/x86/include/asm/refcount.h
  8. +0
    -49
      arch/x86/mm/extable.c
  9. +0
    -1
      drivers/gpu/drm/i915/Kconfig.debug
  10. +58
    -100
      include/linux/refcount.h
  11. +1
    -1
      lib/refcount.c

+ 0
- 21
arch/Kconfig View File

@ -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


+ 0
- 1
arch/arm/Kconfig View File

@ -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


+ 0
- 1
arch/arm64/Kconfig View File

@ -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


+ 0
- 1
arch/s390/configs/debug_defconfig View File

@ -62,7 +62,6 @@ 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


+ 0
- 1
arch/x86/Kconfig View File

@ -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


+ 0
- 6
arch/x86/include/asm/asm.h View File

@ -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


+ 0
- 126
arch/x86/include/asm/refcount.h View File

@ -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

+ 0
- 49
arch/x86/mm/extable.c View File

@ -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)


+ 0
- 1
drivers/gpu/drm/i915/Kconfig.debug View File

@ -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


+ 58
- 100
include/linux/refcount.h View File

@ -1,64 +1,4 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_REFCOUNT_H
#define _LINUX_REFCOUNT_H
#include <linux/atomic.h>
#include <linux/compiler.h>
#include <linux/limits.h>
#include <linux/spinlock_types.h>
struct mutex;
/**
* struct refcount_t - variant of atomic_t specialized for reference counts
* @refs: atomic_t counter field
*
* The counter saturates at REFCOUNT_SATURATED and will not move once
* there. This avoids wrapping the counter and causing 'spurious'
* use-after-free bugs.
*/
typedef struct refcount_struct {
atomic_t refs;
} refcount_t;
#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
#define REFCOUNT_MAX INT_MAX
#define REFCOUNT_SATURATED (INT_MIN / 2)
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
* @r: the refcount
* @n: value to which the refcount will be set
*/
static inline void refcount_set(refcount_t *r, int n)
{
atomic_set(&r->refs, n);
}
/**
* refcount_read - get a refcount's value
* @r: the refcount
*
* Return: the refcount's value
*/
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.
*
@ -136,6 +76,64 @@ static inline unsigned int refcount_read(const refcount_t *r)
*
*/
#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>
struct mutex;
/**
* struct refcount_t - variant of atomic_t specialized for reference counts
* @refs: atomic_t counter field
*
* The counter saturates at REFCOUNT_SATURATED and will not move once
* there. This avoids wrapping the counter and causing 'spurious'
* use-after-free bugs.
*/
typedef struct refcount_struct {
atomic_t refs;
} refcount_t;
#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
#define REFCOUNT_MAX INT_MAX
#define REFCOUNT_SATURATED (INT_MIN / 2)
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
* @r: the refcount
* @n: value to which the refcount will be set
*/
static inline void refcount_set(refcount_t *r, int n)
{
atomic_set(&r->refs, n);
}
/**
* refcount_read - get a refcount's value
* @r: the refcount
*
* Return: the refcount's value
*/
static inline unsigned int refcount_read(const refcount_t *r)
{
return atomic_read(&r->refs);
}
/**
* refcount_add_not_zero - add a value to a refcount unless it is 0
* @i: the value to add to the refcount
@ -298,46 +296,6 @@ 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);


+ 1
- 1
lib/refcount.c View File

@ -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>


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