From nobody Sun Oct 5 19:47:37 2025 Received: from mail-ej1-f74.google.com (mail-ej1-f74.google.com [209.85.218.74]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B71042C3263 for ; Thu, 31 Jul 2025 11:51:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.74 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753962721; cv=none; b=h5RchybX52CDfcxN92emdltslYhsMhW2GanqdqvmuKqRIZdV4L6WGmsffKOThDAJC/OUoOjRcyrBVp+H181ukDJkZm2P0vOaJduTqLndNRIcrp+iIEYX0Jrw6nQcmZVmT3o0qx/4nBhAzkqjRLFrrUJyf0K/22UeCy2JlcGpWo0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753962721; c=relaxed/simple; bh=Tci+SKMZ8RMMxche64nX1uWNAaVUFUvasDdgUwYtAgw=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=oNrJkmk0Bp/kXJcoq9r2Me3idopY3nVSgvrhpjjYmFm15dGTZLhlLl+49qKYvDH7krOk9MolfsaGoyE8mKTNmdUhdXcHdHG5+wzUfwaSxqtp0iqknRsL1bUN63GRlqwTRdo/qT1cbpFSAGkQeSQKQ5ehqWC2iFGhcTHTjtFx8VY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--glider.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=zH+cchL2; arc=none smtp.client-ip=209.85.218.74 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--glider.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="zH+cchL2" Received: by mail-ej1-f74.google.com with SMTP id a640c23a62f3a-af91e018025so50553466b.1 for ; Thu, 31 Jul 2025 04:51:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1753962718; x=1754567518; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=fr3wdyxx9nf1qL2KhZS1xwKvuRnArjYIvI1lmTgg9P0=; b=zH+cchL2HS3OsTWRawLRRt/YHvlpof/dDfdI5qZXpXo/SKybSpwphhCpgJQLgpM+KI vGQEq4YWBtVrRdp5MADXB/rQpMG08X7hxwRdCeac1KucE/zFwih4lG9pth9s6kIzedkA Wg39RSOmBGqm1UDRiPTP5S2ABMv+7xN9veuK1rJpW3voIfx/8D+flwzdoOlfG3zW9bat huit7i2yki96UUxtf9sYx/shrvh+Uh0IKYlK8xb/SxrO7sSD2fzIlxQ2knolb57WP5Nd l7oBsztIbC7ZUEPEjeiUQBx6+MTBCNnqP5WeDrFZNaX/5kxiYdHyCjLOAHMgxLTOSdnh 6JHw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753962718; x=1754567518; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=fr3wdyxx9nf1qL2KhZS1xwKvuRnArjYIvI1lmTgg9P0=; b=FGqLtmyZucwLVIRnhjYQHEPPf8mA2gBXpPlaIpT09Ay6KHOCwwrkpQHcigRNaf8Opa EEngPUz+4qZh9Hij3ZrpjKat2L83Xa5nj3Js6qhZkWirVxTK1KTaMh7nLhs2N0iWlyG2 PYMM3RDhsAzMlYbg+uL/Sg3QO31CwBN/0ufx7sqGvMIxzp3F1fnaT1CbWhCsqFgYkGTU IsBrYJEGGkCt6eq7L49nrgmP4VyKtr67LG3syUHKge0JPQiN0rPN8fZDj+cuC2lwMaLs qlcnQk4nIML5lZ3bu8w8RbkRLCPRCmgyRmcP/pNZroxriamuzv+y75r+p4el7MicZt9y 72lQ== X-Forwarded-Encrypted: i=1; AJvYcCXBxk2uWWdRUMBaIyRrVNEDO40B0SqSavx9ja1qd06AYAHVPrQiGPEJvf210X7VuuvMoQy+9eutYkYJcR4=@vger.kernel.org X-Gm-Message-State: AOJu0YyS011Lm9O8JjlFflGjEMQzRJBoQmMteQ2PXiXZkYY1ENaIIQiB 8lRYZOBAzorwoRMDpF8khQsBkHGyyXd+wOcdzjO5eMQQQcnvGP5pq4qXYROsAO+gNwvdc4T8vjg LMUTnmA== X-Google-Smtp-Source: AGHT+IHv1NYaLHKrEG2v2miqIOvqmDFdLaIEDvxbQ9I1X2gPSxT9NeaOugPde5/hee0pii+5iI9CNX7vL/I= X-Received: from edj19.prod.google.com ([2002:a05:6402:3253:b0:615:979:8d80]) (user=glider job=prod-delivery.src-stubby-dispatcher) by 2002:a17:907:2689:b0:ae3:6cc8:e431 with SMTP id a640c23a62f3a-af8fda6fb17mr960236966b.57.1753962717188; Thu, 31 Jul 2025 04:51:57 -0700 (PDT) Date: Thu, 31 Jul 2025 13:51:34 +0200 In-Reply-To: <20250731115139.3035888-1-glider@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250731115139.3035888-1-glider@google.com> X-Mailer: git-send-email 2.50.1.552.g942d659e1b-goog Message-ID: <20250731115139.3035888-6-glider@google.com> Subject: [PATCH v4 05/10] kcov: x86: introduce CONFIG_KCOV_UNIQUE From: Alexander Potapenko To: glider@google.com Cc: quic_jiangenj@quicinc.com, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, x86@kernel.org, Dmitry Vyukov , Aleksandr Nogikh , Andrey Konovalov , Borislav Petkov , Dave Hansen , Ingo Molnar , Josh Poimboeuf , Marco Elver , Peter Zijlstra , Thomas Gleixner Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The new config switches coverage instrumentation to using __sanitizer_cov_trace_pc_guard(u32 *guard) instead of __sanitizer_cov_trace_pc(void) This relies on Clang's -fsanitize-coverage=3Dtrace-pc-guard flag [1]. Each callback receives a unique 32-bit guard variable residing in .bss. Those guards can be used by kcov to deduplicate the coverage on the fly. As a first step, we make the new instrumentation mode 1:1 compatible with the old one. [1] https://clang.llvm.org/docs/SanitizerCoverage.html#tracing-pcs-with-gua= rds Cc: x86@kernel.org Signed-off-by: Alexander Potapenko Reviewed-by: Dmitry Vyukov --- v4: - add Reviewed-by: Dmitry Vyukov v3: - per Dmitry Vyukov's request, add better comments in scripts/module.lds.S and lib/Kconfig.debug - add -sanitizer-coverage-drop-ctors to scripts/Makefile.kcov to drop the unwanted constructors emitting unsupported relocations - merge the __sancov_guards section into .bss v2: - Address comments by Dmitry Vyukov - rename CONFIG_KCOV_ENABLE_GUARDS to CONFIG_KCOV_UNIQUE - update commit description and config description - Address comments by Marco Elver - rename sanitizer_cov_write_subsequent() to kcov_append_to_buffer() - make config depend on X86_64 (via ARCH_HAS_KCOV_UNIQUE) - swap #ifdef branches - tweak config description - remove redundant check for CONFIG_CC_HAS_SANCOV_TRACE_PC_GUARD Change-Id: Iacb1e71fd061a82c2acadf2347bba4863b9aec39 --- arch/x86/Kconfig | 1 + arch/x86/kernel/vmlinux.lds.S | 1 + include/asm-generic/vmlinux.lds.h | 13 ++++++- include/linux/kcov.h | 2 + kernel/kcov.c | 61 +++++++++++++++++++++---------- lib/Kconfig.debug | 26 +++++++++++++ scripts/Makefile.kcov | 7 ++++ scripts/module.lds.S | 35 ++++++++++++++++++ tools/objtool/check.c | 1 + 9 files changed, 126 insertions(+), 21 deletions(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 8bed9030ad473..0533070d24fe7 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -94,6 +94,7 @@ config X86 select ARCH_HAS_FORTIFY_SOURCE select ARCH_HAS_GCOV_PROFILE_ALL select ARCH_HAS_KCOV if X86_64 + select ARCH_HAS_KCOV_UNIQUE if X86_64 select ARCH_HAS_KERNEL_FPU_SUPPORT select ARCH_HAS_MEM_ENCRYPT select ARCH_HAS_MEMBARRIER_SYNC_CORE diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 4fa0be732af10..52fe6539b9c91 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -372,6 +372,7 @@ SECTIONS . =3D ALIGN(PAGE_SIZE); *(BSS_MAIN) BSS_DECRYPTED + BSS_SANCOV_GUARDS . =3D ALIGN(PAGE_SIZE); __bss_stop =3D .; } diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinu= x.lds.h index fa5f19b8d53a0..ee78328eecade 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -102,7 +102,8 @@ * sections to be brought in with rodata. */ #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CL= ANG) || \ -defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) + defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG) || \ + defined(CONFIG_KCOV_UNIQUE) #define TEXT_MAIN .text .text.[0-9a-zA-Z_]* #else #define TEXT_MAIN .text @@ -121,6 +122,16 @@ defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPEL= LER_CLANG) #define SBSS_MAIN .sbss #endif =20 +#if defined(CONFIG_KCOV_UNIQUE) +/* BSS_SANCOV_GUARDS must be part of the .bss section so that it is zero-i= nitialized. */ +#define BSS_SANCOV_GUARDS \ + __start___sancov_guards =3D .; \ + *(__sancov_guards); \ + __stop___sancov_guards =3D .; +#else +#define BSS_SANCOV_GUARDS +#endif + /* * GCC 4.5 and later have a 32 bytes section alignment for structures. * Except GCC 4.9, that feels the need to align on 64 bytes. diff --git a/include/linux/kcov.h b/include/linux/kcov.h index 2b3655c0f2278..2acccfa5ae9af 100644 --- a/include/linux/kcov.h +++ b/include/linux/kcov.h @@ -107,6 +107,8 @@ typedef unsigned long long kcov_u64; #endif =20 void __sanitizer_cov_trace_pc(void); +void __sanitizer_cov_trace_pc_guard(u32 *guard); +void __sanitizer_cov_trace_pc_guard_init(uint32_t *start, uint32_t *stop); void __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2); void __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2); void __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2); diff --git a/kernel/kcov.c b/kernel/kcov.c index 5170f367c8a1b..8154ac1c1622e 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -194,27 +194,15 @@ static notrace unsigned long canonicalize_ip(unsigned= long ip) return ip; } =20 -/* - * Entry point from instrumented code. - * This is called once per basic-block/edge. - */ -void notrace __sanitizer_cov_trace_pc(void) +static notrace void kcov_append_to_buffer(unsigned long *area, int size, + unsigned long ip) { - struct task_struct *t; - unsigned long *area; - unsigned long ip =3D canonicalize_ip(_RET_IP_); - unsigned long pos; - - t =3D current; - if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t)) - return; - - area =3D t->kcov_state.area; /* The first 64-bit word is the number of subsequent PCs. */ - pos =3D READ_ONCE(area[0]) + 1; - if (likely(pos < t->kcov_state.size)) { - /* Previously we write pc before updating pos. However, some - * early interrupt code could bypass check_kcov_mode() check + unsigned long pos =3D READ_ONCE(area[0]) + 1; + + if (likely(pos < size)) { + /* + * Some early interrupt code could bypass check_kcov_mode() check * and invoke __sanitizer_cov_trace_pc(). If such interrupt is * raised between writing pc and updating pos, the pc could be * overitten by the recursive __sanitizer_cov_trace_pc(). @@ -225,7 +213,40 @@ void notrace __sanitizer_cov_trace_pc(void) area[pos] =3D ip; } } + +/* + * Entry point from instrumented code. + * This is called once per basic-block/edge. + */ +#ifdef CONFIG_KCOV_UNIQUE +void notrace __sanitizer_cov_trace_pc_guard(u32 *guard) +{ + if (!check_kcov_mode(KCOV_MODE_TRACE_PC, current)) + return; + + kcov_append_to_buffer(current->kcov_state.area, + current->kcov_state.size, + canonicalize_ip(_RET_IP_)); +} +EXPORT_SYMBOL(__sanitizer_cov_trace_pc_guard); + +void notrace __sanitizer_cov_trace_pc_guard_init(uint32_t *start, + uint32_t *stop) +{ +} +EXPORT_SYMBOL(__sanitizer_cov_trace_pc_guard_init); +#else /* !CONFIG_KCOV_UNIQUE */ +void notrace __sanitizer_cov_trace_pc(void) +{ + if (!check_kcov_mode(KCOV_MODE_TRACE_PC, current)) + return; + + kcov_append_to_buffer(current->kcov_state.area, + current->kcov_state.size, + canonicalize_ip(_RET_IP_)); +} EXPORT_SYMBOL(__sanitizer_cov_trace_pc); +#endif =20 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip) @@ -253,7 +274,7 @@ static void notrace write_comp_data(u64 type, u64 arg1,= u64 arg2, u64 ip) start_index =3D 1 + count * KCOV_WORDS_PER_CMP; end_pos =3D (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64); if (likely(end_pos <=3D max_pos)) { - /* See comment in __sanitizer_cov_trace_pc(). */ + /* See comment in kcov_append_to_buffer(). */ WRITE_ONCE(area[0], count + 1); barrier(); area[start_index] =3D type; diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index ebe33181b6e6e..a7441f89465f3 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2153,6 +2153,12 @@ config ARCH_HAS_KCOV build and run with CONFIG_KCOV. This typically requires disabling instrumentation for some early boot code. =20 +config CC_HAS_SANCOV_TRACE_PC + def_bool $(cc-option,-fsanitize-coverage=3Dtrace-pc) + +config CC_HAS_SANCOV_TRACE_PC_GUARD + def_bool $(cc-option,-fsanitize-coverage=3Dtrace-pc-guard) + config KCOV bool "Code coverage for fuzzing" depends on ARCH_HAS_KCOV @@ -2166,6 +2172,26 @@ config KCOV =20 For more details, see Documentation/dev-tools/kcov.rst. =20 +config ARCH_HAS_KCOV_UNIQUE + bool + help + An architecture should select this when it can successfully + build and run with CONFIG_KCOV_UNIQUE. + +config KCOV_UNIQUE + depends on KCOV + depends on CC_HAS_SANCOV_TRACE_PC_GUARD && ARCH_HAS_KCOV_UNIQUE + bool "Enable unique program counter collection mode for KCOV" + help + This option enables KCOV's unique program counter (PC) collection mode, + which deduplicates PCs on the fly when the KCOV_UNIQUE_ENABLE ioctl is + used. + + This significantly reduces the memory footprint for coverage data + collection compared to trace mode, as it prevents the kernel from + storing the same PC multiple times. + Enabling this mode incurs a slight increase in kernel binary size. + config KCOV_ENABLE_COMPARISONS bool "Enable comparison operands collection by KCOV" depends on KCOV diff --git a/scripts/Makefile.kcov b/scripts/Makefile.kcov index 78305a84ba9d2..c3ad5504f5600 100644 --- a/scripts/Makefile.kcov +++ b/scripts/Makefile.kcov @@ -1,5 +1,12 @@ # SPDX-License-Identifier: GPL-2.0-only +ifeq ($(CONFIG_KCOV_UNIQUE),y) +kcov-flags-y +=3D -fsanitize-coverage=3Dtrace-pc-guard +# Drop per-file constructors that -fsanitize-coverage=3Dtrace-pc-guard ins= erts by default. +# Kernel does not need them, and they may produce unknown relocations. +kcov-flags-y +=3D -mllvm -sanitizer-coverage-drop-ctors +else kcov-flags-y +=3D -fsanitize-coverage=3Dtrace-pc +endif kcov-flags-$(CONFIG_KCOV_ENABLE_COMPARISONS) +=3D -fsanitize-coverage=3Dtr= ace-cmp =20 kcov-rflags-y +=3D -Cpasses=3Dsancov-module diff --git a/scripts/module.lds.S b/scripts/module.lds.S index 450f1088d5fd3..17f36d5112c5d 100644 --- a/scripts/module.lds.S +++ b/scripts/module.lds.S @@ -47,6 +47,7 @@ SECTIONS { .bss : { *(.bss .bss.[0-9a-zA-Z_]*) *(.bss..L*) + *(__sancov_guards) } =20 .data : { @@ -64,6 +65,40 @@ SECTIONS { MOD_CODETAG_SECTIONS() } #endif + +#ifdef CONFIG_KCOV_UNIQUE + /* + * CONFIG_KCOV_UNIQUE creates COMDAT groups for instrumented functions, + * which has the following consequences in the presence of + * -ffunction-sections: + * - Separate .init.text and .exit.text sections in the modules are not + * merged together, which results in errors trying to create + * duplicate entries in /sys/module/MODNAME/sections/ at module load + * time. + * - Each function is placed in a separate .text.funcname section, so + * there is no .text section anymore. Collecting them together here + * has mostly aesthetic purpose, although some tools may be expecting + * it to be present. + */ + .text : { + *(.text .text.[0-9a-zA-Z_]*) + *(.text..L*) + } + .init.text : { + *(.init.text .init.text.[0-9a-zA-Z_]*) + *(.init.text..L*) + } + .exit.text : { + *(.exit.text .exit.text.[0-9a-zA-Z_]*) + *(.exit.text..L*) + } + .bss : { + *(.bss .bss.[0-9a-zA-Z_]*) + *(.bss..L*) + *(__sancov_guards) + } +#endif + MOD_SEPARATE_CODETAG_SECTIONS() } =20 diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 67d76f3a1dce5..60eb5faa27d28 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1156,6 +1156,7 @@ static const char *uaccess_safe_builtin[] =3D { "write_comp_data", "check_kcov_mode", "__sanitizer_cov_trace_pc", + "__sanitizer_cov_trace_pc_guard", "__sanitizer_cov_trace_const_cmp1", "__sanitizer_cov_trace_const_cmp2", "__sanitizer_cov_trace_const_cmp4", --=20 2.50.1.552.g942d659e1b-goog