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Message-Id: <20170725181536.21092-1-ard.biesheuvel@linaro.org> Date: Tue, 25 Jul 2017 19:15:36 +0100 From: Ard Biesheuvel <ard.biesheuvel@...aro.org> To: linux-arm-kernel@...ts.infradead.org, kernel-hardening@...ts.openwall.com Cc: will.deacon@....com, keescook@...omium.org, mark.rutland@....com, labbott@...oraproject.org, hw.likun@...wei.com, Ard Biesheuvel <ard.biesheuvel@...aro.org> Subject: [PATCH v2] arm64: kernel: implement fast refcount checking This adds support to arm64 for fast refcount checking, as proposed by Kees for x86 based on the implementation by grsecurity/PaX. The general approach is identical: the existing atomic_t helpers are cloned for refcount_t, with a single branch instruction added that jumps to an out of line handler if overflow and/or decrement to zero is detected. One complication that we have to deal with on arm64 is the fact that is has two atomics implementations: the original LL/SC implementation using load/store exclusive loops, and the newer LSE one that do mostly the same in a single instruction. So we need to clone some parts of both for the refcount handlers, but we also need to deal with the way LSE builds fall back to LL/SC at runtime if the hardware does not support it. Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org> --- This is a quick v2 after I sent the original RFC patch only 6 hours ago. However, as Kees pointed out, it appears I am not the only person looking into this for arm64, and so it makes sense to share my latest before going on travel for the rest of the week. v2: - Avoid adrp instructions, it does not always work in modules. Instead, use a 32-bit offset in the out-of-line sequence that we can dereference in the handler. - Use release semantics for sub/dec - Switch to b.mi / b.ls which better matches the x86 code (we don't actually detect signed overflow, i.e., from 0x7fffffff to 0x80000000) - Write a commit log Now tested using lkdtm: not all tests work as expected (the SATURATE ones seem broken) but Kees has this covered already. arch/arm64/Kconfig | 1 + arch/arm64/include/asm/atomic.h | 15 ++++ arch/arm64/include/asm/atomic_ll_sc.h | 28 +++++++ arch/arm64/include/asm/atomic_lse.h | 52 ++++++++++++ arch/arm64/include/asm/brk-imm.h | 1 + arch/arm64/include/asm/refcount.h | 88 ++++++++++++++++++++ arch/arm64/kernel/traps.c | 37 ++++++++ arch/arm64/lib/atomic_ll_sc.c | 6 ++ 8 files changed, 228 insertions(+) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index dfd908630631..53b9a8f5277b 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -16,6 +16,7 @@ config ARM64 select ARCH_HAS_GCOV_PROFILE_ALL select ARCH_HAS_GIGANTIC_PAGE if (MEMORY_ISOLATION && COMPACTION) || CMA select ARCH_HAS_KCOV + select ARCH_HAS_REFCOUNT select ARCH_HAS_SET_MEMORY select ARCH_HAS_SG_CHAIN select ARCH_HAS_STRICT_KERNEL_RWX diff --git a/arch/arm64/include/asm/atomic.h b/arch/arm64/include/asm/atomic.h index c0235e0ff849..93a0313ab0ae 100644 --- a/arch/arm64/include/asm/atomic.h +++ b/arch/arm64/include/asm/atomic.h @@ -24,10 +24,25 @@ #include <linux/types.h> #include <asm/barrier.h> +#include <asm/brk-imm.h> #include <asm/lse.h> #ifdef __KERNEL__ +#define REFCOUNT_CHECK(cond) \ +"22: b." #cond " 33f\n" \ +" .pushsection \".text.unlikely\"\n" \ +"33: mov x16, %[counter]\n" \ +" adr x17, 44f\n" \ +" brk %[brk_imm]\n" \ +"44: .long 22b - .\n" \ +" .popsection\n" + +#define REFCOUNT_INPUTS(r) \ + [counter] "r" (&(r)->counter), [brk_imm] "i" (REFCOUNT_BRK_IMM), + +#define REFCOUNT_CLOBBERS : "cc", "x16", "x17" + #define __ARM64_IN_ATOMIC_IMPL #if defined(CONFIG_ARM64_LSE_ATOMICS) && defined(CONFIG_AS_LSE) diff --git a/arch/arm64/include/asm/atomic_ll_sc.h b/arch/arm64/include/asm/atomic_ll_sc.h index f5a2d09afb38..99d0beb70ef1 100644 --- a/arch/arm64/include/asm/atomic_ll_sc.h +++ b/arch/arm64/include/asm/atomic_ll_sc.h @@ -327,4 +327,32 @@ __CMPXCHG_DBL(_mb, dmb ish, l, "memory") #undef __CMPXCHG_DBL +#define REFCOUNT_OP(op, asm_op, cond, l, clobber...) \ +__LL_SC_INLINE int \ +__LL_SC_PREFIX(__refcount_##op(int i, atomic_t *r)) \ +{ \ + unsigned long tmp; \ + int result; \ + \ + asm volatile("// refcount_" #op "\n" \ +" prfm pstl1strm, %2\n" \ +"1: ldxr %w0, %2\n" \ +" " #asm_op " %w0, %w0, %w[i]\n" \ +" st" #l "xr %w1, %w0, %2\n" \ +" cbnz %w1, 1b\n" \ + REFCOUNT_CHECK(cond) \ + : "=&r" (result), "=&r" (tmp), "+Q" (r->counter) \ + : REFCOUNT_INPUTS(r) [i] "Ir" (i) \ + clobber); \ + \ + return result; \ +} \ +__LL_SC_EXPORT(__refcount_##op); + +REFCOUNT_OP(add_lt, adds, mi, , REFCOUNT_CLOBBERS); +REFCOUNT_OP(sub_lt_neg, adds, mi, l, REFCOUNT_CLOBBERS); +REFCOUNT_OP(sub_le_neg, adds, ls, l, REFCOUNT_CLOBBERS); +REFCOUNT_OP(sub_lt, subs, mi, l, REFCOUNT_CLOBBERS); +REFCOUNT_OP(sub_le, subs, ls, l, REFCOUNT_CLOBBERS); + #endif /* __ASM_ATOMIC_LL_SC_H */ diff --git a/arch/arm64/include/asm/atomic_lse.h b/arch/arm64/include/asm/atomic_lse.h index 99fa69c9c3cf..0551dfe6679a 100644 --- a/arch/arm64/include/asm/atomic_lse.h +++ b/arch/arm64/include/asm/atomic_lse.h @@ -531,4 +531,56 @@ __CMPXCHG_DBL(_mb, al, "memory") #undef __LL_SC_CMPXCHG_DBL #undef __CMPXCHG_DBL +#define REFCOUNT_ADD_OP(op, rel, cond) \ +static inline int __refcount_##op(int i, atomic_t *r) \ +{ \ + register int w0 asm ("w0") = i; \ + register atomic_t *x1 asm ("x1") = r; \ + \ + asm volatile(ARM64_LSE_ATOMIC_INSN( \ + /* LL/SC */ \ + __LL_SC_CALL(__refcount_##op) \ + __nops(1), \ + /* LSE atomics */ \ + " ldadd" #rel " %w[i], w30, %[v]\n" \ + " adds %w[i], %w[i], w30") \ + REFCOUNT_CHECK(cond) \ + : [i] "+r" (w0), [v] "+Q" (r->counter) \ + : REFCOUNT_INPUTS(r) "r" (x1) \ + : __LL_SC_CLOBBERS, "cc"); \ + \ + return w0; \ +} + +#define REFCOUNT_SUB_OP(op, cond, fbop) \ +static inline int __refcount_##op(int i, atomic_t *r) \ +{ \ + register int w0 asm ("w0") = i; \ + register atomic_t *x1 asm ("x1") = r; \ + \ + if (__builtin_constant_p(i)) \ + return __refcount_##fbop(-i, r); \ + \ + asm volatile(ARM64_LSE_ATOMIC_INSN( \ + /* LL/SC */ \ + __LL_SC_CALL(__refcount_##op) \ + __nops(2), \ + /* LSE atomics */ \ + " neg %w[i], %w[i]\n" \ + " ldaddl %w[i], w30, %[v]\n" \ + " adds %w[i], %w[i], w30") \ + REFCOUNT_CHECK(cond) \ + : [i] "+r" (w0), [v] "+Q" (r->counter) \ + : REFCOUNT_INPUTS(r) "r" (x1) \ + : __LL_SC_CLOBBERS, "cc"); \ + \ + return w0; \ +} + +REFCOUNT_ADD_OP(add_lt, , mi); +REFCOUNT_ADD_OP(sub_lt_neg, l, mi); +REFCOUNT_ADD_OP(sub_le_neg, l, ls); +REFCOUNT_SUB_OP(sub_lt, mi, sub_lt_neg); +REFCOUNT_SUB_OP(sub_le, ls, sub_le_neg); + #endif /* __ASM_ATOMIC_LSE_H */ diff --git a/arch/arm64/include/asm/brk-imm.h b/arch/arm64/include/asm/brk-imm.h index ed693c5bcec0..0bce57737ff1 100644 --- a/arch/arm64/include/asm/brk-imm.h +++ b/arch/arm64/include/asm/brk-imm.h @@ -18,6 +18,7 @@ * 0x800: kernel-mode BUG() and WARN() traps */ #define FAULT_BRK_IMM 0x100 +#define REFCOUNT_BRK_IMM 0x101 #define KGDB_DYN_DBG_BRK_IMM 0x400 #define KGDB_COMPILED_DBG_BRK_IMM 0x401 #define BUG_BRK_IMM 0x800 diff --git a/arch/arm64/include/asm/refcount.h b/arch/arm64/include/asm/refcount.h new file mode 100644 index 000000000000..575c199cb34a --- /dev/null +++ b/arch/arm64/include/asm/refcount.h @@ -0,0 +1,88 @@ +/* + * arm64-specific implementation of refcount_t. Based on x86 version and + * PAX_REFCOUNT from PaX/grsecurity. + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + */ + +#ifndef __ASM_REFCOUNT_H +#define __ASM_REFCOUNT_H + +#include <linux/refcount.h> + +#include <asm/atomic.h> +#include <asm/uaccess.h> + +static __always_inline void refcount_add(int i, refcount_t *r) +{ + __refcount_add_lt(i, &r->refs); +} + +static __always_inline void refcount_inc(refcount_t *r) +{ + __refcount_add_lt(1, &r->refs); +} + +static __always_inline void refcount_dec(refcount_t *r) +{ + __refcount_sub_le(1, &r->refs); +} + +static __always_inline __must_check bool refcount_sub_and_test(unsigned int i, + refcount_t *r) +{ + return __refcount_sub_lt(i, &r->refs) == 0; +} + +static __always_inline __must_check bool refcount_dec_and_test(refcount_t *r) +{ + return __refcount_sub_lt(1, &r->refs) == 0; +} + +/** + * __refcount_add_unless - add unless the number is already a given value + * @r: pointer of type refcount_t + * @a: the amount to add to v... + * @u: ...unless v is equal to u. + * + * Atomically adds @a to @r, so long as @r was not already @u. + * Returns the old value of @r. + */ +static __always_inline __must_check int __refcount_add_unless(refcount_t *r, + int a, int u) +{ + int c, new; + + c = atomic_read(&(r->refs)); + do { + if (unlikely(c == u)) + break; + + asm volatile( + "adds %0, %0, %2 ;" + REFCOUNT_CHECK(lt) + : "=r" (new) + : "0" (c), "Ir" (a), + [counter] "r" (&r->refs.counter), + [brk_imm] "i" (REFCOUNT_BRK_IMM) + : "cc", "x16", "x17"); + + } while (!atomic_try_cmpxchg(&(r->refs), &c, new)); + + return c; +} + +static __always_inline __must_check +bool refcount_add_not_zero(unsigned int i, refcount_t *r) +{ + return __refcount_add_unless(r, i, 0) != 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/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index c7c7088097be..69040206a559 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -758,8 +758,45 @@ int __init early_brk64(unsigned long addr, unsigned int esr, return bug_handler(regs, esr) != DBG_HOOK_HANDLED; } +static int refcount_overflow_handler(struct pt_regs *regs, unsigned int esr) +{ + /* First unconditionally saturate the refcount. */ + *(int *)regs->regs[16] = INT_MIN / 2; + + /* + * 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(). + * + * Duplicate the condition check against PSTATE based on the + * instructions that could have brought us here: + * + * b.mi => N == 1 + * b.ls => C == 0 || Z == 1 + */ + if (regs->pstate & (PSR_N_BIT | PSR_Z_BIT) || + !(regs->pstate & PSR_C_BIT)) { + bool zero = regs->pstate & PSR_Z_BIT; + + /* point pc to the branch instruction that brought us here */ + regs->pc = regs->regs[17] + *(s32 *)regs->regs[17]; + refcount_error_report(regs, zero ? "hit zero" : "overflow"); + } + + /* advance pc and proceed */ + regs->pc += 4; + return DBG_HOOK_HANDLED; +} + +static struct break_hook refcount_break_hook = { + .esr_val = 0xf2000000 | REFCOUNT_BRK_IMM, + .esr_mask = 0xffffffff, + .fn = refcount_overflow_handler, +}; + /* This registration must happen early, before debug_traps_init(). */ void __init trap_init(void) { register_break_hook(&bug_break_hook); + register_break_hook(&refcount_break_hook); } diff --git a/arch/arm64/lib/atomic_ll_sc.c b/arch/arm64/lib/atomic_ll_sc.c index b0c538b0da28..5f038abdc635 100644 --- a/arch/arm64/lib/atomic_ll_sc.c +++ b/arch/arm64/lib/atomic_ll_sc.c @@ -1,3 +1,9 @@ #include <asm/atomic.h> #define __ARM64_IN_ATOMIC_IMPL +#undef REFCOUNT_CHECK +#undef REFCOUNT_INPUTS +#undef REFCOUNT_CLOBBERS +#define REFCOUNT_CHECK(cond) +#define REFCOUNT_INPUTS(r) +#define REFCOUNT_CLOBBERS : "cc" #include <asm/atomic_ll_sc.h> -- 2.9.3
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