From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751550AbeFDSiS (ORCPT ); Mon, 4 Jun 2018 14:38:18 -0400 Received: from ex13-edg-ou-002.vmware.com ([208.91.0.190]:51805 "EHLO EX13-EDG-OU-002.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750985AbeFDSg2 (ORCPT ); Mon, 4 Jun 2018 14:36:28 -0400 From: Nadav Amit To: , CC: Nadav Amit , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Kees Cook , Jan Beulich , Josh Poimboeuf Subject: [PATCH v2 3/9] x86: refcount: prevent gcc distortions Date: Mon, 4 Jun 2018 04:21:25 -0700 Message-ID: <20180604112131.59100-4-namit@vmware.com> X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180604112131.59100-1-namit@vmware.com> References: <20180604112131.59100-1-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org GCC considers the number of statements in inlined assembly blocks, according to new-lines and semicolons, as an indication to the cost of the block in time and space. This data is distorted by the kernel code, which puts information in alternative sections. As a result, the compiler may perform incorrect inlining and branch optimizations. The solution is to set an assembly macro and call it from the inlined assembly block. As a result GCC considers the inline assembly block as a single instruction. This patch allows to inline functions such as __get_seccomp_filter(). Interestingly, this allows more aggressive inlining while reducing the kernel size. text data bss dec hex filename 18140970 10225412 2957312 31323694 1ddf62e ./vmlinux before 18140140 10225284 2957312 31322736 1ddf270 ./vmlinux after (-958) Static text symbols: Before: 40302 After: 40286 (-16) Functions such as kref_get(), free_user(), fuse_file_get() now get inlined. Cc: Thomas Gleixner Cc: Ingo Molnar Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: Kees Cook Cc: Jan Beulich Cc: Josh Poimboeuf Signed-off-by: Nadav Amit --- arch/x86/include/asm/refcount.h | 73 ++++++++++++++++++++------------- arch/x86/kernel/macros.S | 1 + 2 files changed, 45 insertions(+), 29 deletions(-) diff --git a/arch/x86/include/asm/refcount.h b/arch/x86/include/asm/refcount.h index 4cf11d88d3b3..53462f32b58e 100644 --- a/arch/x86/include/asm/refcount.h +++ b/arch/x86/include/asm/refcount.h @@ -4,6 +4,9 @@ * x86-specific implementation of refcount_t. Based on PAX_REFCOUNT from * PaX/grsecurity. */ + +#ifndef __ASSEMBLY__ + #include /* @@ -14,34 +17,11 @@ * 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 %[counter], %%" _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 + "REFCOUNT_CHECK_LT_ZERO counter=\"%[counter]\"" : [counter] "+m" (r->refs.counter) : "ir" (i) : "cc", "cx"); @@ -50,7 +30,7 @@ static __always_inline void refcount_add(unsigned int i, refcount_t *r) static __always_inline void refcount_inc(refcount_t *r) { asm volatile(LOCK_PREFIX "incl %0\n\t" - REFCOUNT_CHECK_LT_ZERO + "REFCOUNT_CHECK_LT_ZERO counter=\"%[counter]\"" : [counter] "+m" (r->refs.counter) : : "cc", "cx"); } @@ -58,7 +38,7 @@ static __always_inline void refcount_inc(refcount_t *r) static __always_inline void refcount_dec(refcount_t *r) { asm volatile(LOCK_PREFIX "decl %0\n\t" - REFCOUNT_CHECK_LE_ZERO + "REFCOUNT_CHECK_LE_ZERO counter=\"%[counter]\"" : [counter] "+m" (r->refs.counter) : : "cc", "cx"); } @@ -66,13 +46,15 @@ static __always_inline void refcount_dec(refcount_t *r) static __always_inline __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r) { - GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl", REFCOUNT_CHECK_LT_ZERO, + GEN_BINARY_SUFFIXED_RMWcc(LOCK_PREFIX "subl", + "REFCOUNT_CHECK_LT_ZERO counter=\"%0\"", r->refs.counter, "er", i, "%0", e, "cx"); } static __always_inline __must_check bool refcount_dec_and_test(refcount_t *r) { - GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl", REFCOUNT_CHECK_LT_ZERO, + GEN_UNARY_SUFFIXED_RMWcc(LOCK_PREFIX "decl", + "REFCOUNT_CHECK_LT_ZERO counter=\"%0\"", r->refs.counter, "%0", e, "cx"); } @@ -90,7 +72,7 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r) /* Did we try to increment from/to an undesirable state? */ if (unlikely(c < 0 || c == INT_MAX || result < c)) { - asm volatile(REFCOUNT_ERROR + asm volatile("REFCOUNT_ERROR counter=\"%[counter]\"" : : [counter] "m" (r->refs.counter) : "cc", "cx"); break; @@ -106,4 +88,37 @@ static __always_inline __must_check bool refcount_inc_not_zero(refcount_t *r) return refcount_add_not_zero(1, r); } +#else /* __ASSEMBLY__ */ +#include +#include + +.macro REFCOUNT_EXCEPTION counter:req + .pushsection .text..refcount +111: lea \counter, %_ASM_CX +112: ud2 + ASM_UNREACHABLE + .popsection +113: _ASM_EXTABLE_REFCOUNT(112b, 113b) +.endm + +/* Trigger refcount exception if refcount result is negative. */ +.macro REFCOUNT_CHECK_LT_ZERO counter:req + js 111f + REFCOUNT_EXCEPTION \counter +.endm + +/* Trigger refcount exception if refcount result is zero or negative. */ +.macro REFCOUNT_CHECK_LE_ZERO counter:req + jz 111f + REFCOUNT_CHECK_LT_ZERO counter=\counter +.endm + +/* Trigger refcount exception unconditionally. */ +.macro REFCOUNT_ERROR counter:req + jmp 111f + REFCOUNT_EXCEPTION counter=\counter +.endm + +#endif /* __ASSEMBLY__ */ + #endif diff --git a/arch/x86/kernel/macros.S b/arch/x86/kernel/macros.S index cee28c3246dc..f1fe1d570365 100644 --- a/arch/x86/kernel/macros.S +++ b/arch/x86/kernel/macros.S @@ -7,3 +7,4 @@ */ #include +#include -- 2.17.0