From patchwork Tue Jan 26 17:10:43 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ard Biesheuvel X-Patchwork-Id: 60486 Delivered-To: patch@linaro.org Received: by 10.112.130.2 with SMTP id oa2csp2089043lbb; Tue, 26 Jan 2016 09:12:03 -0800 (PST) X-Received: by 10.98.10.203 with SMTP id 72mr35494798pfk.87.1453828314113; Tue, 26 Jan 2016 09:11:54 -0800 (PST) Return-Path: Received: from vger.kernel.org (vger.kernel.org. [209.132.180.67]) by mx.google.com with ESMTP id wb3si3082437pab.114.2016.01.26.09.11.53; Tue, 26 Jan 2016 09:11:54 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dkim=pass header.i=@linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967102AbcAZRLu (ORCPT + 30 others); Tue, 26 Jan 2016 12:11:50 -0500 Received: from mail-wm0-f44.google.com ([74.125.82.44]:37410 "EHLO mail-wm0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934100AbcAZRLn (ORCPT ); Tue, 26 Jan 2016 12:11:43 -0500 Received: by mail-wm0-f44.google.com with SMTP id n5so141760674wmn.0 for ; Tue, 26 Jan 2016 09:11:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=DgtSPjtIe712O8tPL+U/pqZFnW+ptH5mtO5Ssyw3E9M=; b=YUQeukDl/3LJARJLHPBkOMJvNRfAntqjJVFR73OxNf+FBac98XuswTcnt4FeOTe802 aMaOa5Il8MSz8BmInuvxsKuorQ2AeiTkgPYSFBC3cyn4Fd5/hvnDX2zdsEHkzW4w4HTp q2qmE1T51eO8htAcdnNsfqNfhaazbuivjSgYY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=DgtSPjtIe712O8tPL+U/pqZFnW+ptH5mtO5Ssyw3E9M=; b=mnfTP/JsJmL1pXuaKfbAP9rBb9GuXCy6BoW4GzLq7PSXok99bM6Ji3Fdq3ixxAmrxq J4PA01kvGH+S5o632rlAZvwseW07GLO1RVd6okE1Dw0II06bS5R9JDv7dm9VIT9M2bM8 bULcmhHZOH4cFREXuefU5TKFM0Jc4kgafX/xlLTZrSlczN9lITiPN8lWiAto4sLd5m3w H0Ex7SMWYROHxbPvHQqXKF6fa2j/gzcyGXZkhJLWs3CUvDOHFtHnDji0iGRpzou7EUaQ XlBCxPUQidXoLy1oPfji+6C+Ll6NJMpUQHUZZ6BNmmW9sSchE+xQlkJ1x0r4yozIfrVN YYVg== X-Gm-Message-State: AG10YOSNVjuPdScW2YWaxeG8HGmb/R5Q8cVh0XLCe1KnanGf9et+OcqlfuZNKDECvp6zyHTv X-Received: by 10.194.171.66 with SMTP id as2mr24470510wjc.73.1453828302059; Tue, 26 Jan 2016 09:11:42 -0800 (PST) Received: from localhost.localdomain ([195.55.142.58]) by smtp.gmail.com with ESMTPSA id ko2sm2328617wjc.9.2016.01.26.09.11.38 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 26 Jan 2016 09:11:40 -0800 (PST) From: Ard Biesheuvel To: linux-arm-kernel@lists.infradead.org, kernel-hardening@lists.openwall.com, will.deacon@arm.com, catalin.marinas@arm.com, mark.rutland@arm.com, leif.lindholm@linaro.org, keescook@chromium.org, linux-kernel@vger.kernel.org Cc: stuart.yoder@freescale.com, bhupesh.sharma@freescale.com, arnd@arndb.de, marc.zyngier@arm.com, christoffer.dall@linaro.org, labbott@fedoraproject.org, matt@codeblueprint.co.uk, Ard Biesheuvel , Heiko Carstens , Michael Ellerman , Ingo Molnar , "H. Peter Anvin" , Benjamin Herrenschmidt , Michal Marek , Rusty Russell , Andrew Morton Subject: [PATCH v4 16/22] kallsyms: add support for relative offsets in kallsyms address table Date: Tue, 26 Jan 2016 18:10:43 +0100 Message-Id: <1453828249-14467-17-git-send-email-ard.biesheuvel@linaro.org> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1453828249-14467-1-git-send-email-ard.biesheuvel@linaro.org> References: <1453828249-14467-1-git-send-email-ard.biesheuvel@linaro.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Similar to how relative extables are implemented, it is possible to emit the kallsyms table in such a way that it contains offsets relative to some anchor point in the kernel image rather than absolute addresses. On 64-bit architectures, it cuts the size of the kallsyms address table in half, since offsets between kernel symbols can typically be expressed in 32 bits. This saves several hundreds of kilobytes of permanent .rodata on average. In addition, the kallsyms address table is no longer subject to dynamic relocation when CONFIG_RELOCATABLE is in effect, so the relocation work done after decompression now doesn't have to do relocation updates for all these values. This saves up to 24 bytes (i.e., the size of a ELF64 RELA relocation table entry) per value, which easily adds up to a couple of megabytes of uncompressed __init data on ppc64 or arm64. Even if these relocation entries typically compress well, the combined size reduction of 2.8 MB uncompressed for a ppc64_defconfig build (of which 2.4 MB is __init data) results in a ~500 KB space saving in the compressed image. Since it is useful for some architectures (like x86) to retain the ability to emit absolute values as well, this patch adds support for both, by emitting absolute addresses as positive 32-bit values, and addresses relative to the lowest encountered relative symbol as negative values, which are subtracted from the runtime address of this base symbol to produce the actual address. Support for the above is enabled by default for all architectures except IA-64, whose symbols are too far apart to capture in this manner. Signed-off-by: Ard Biesheuvel Tested-by: Guenter Roeck Reviewed-by: Kees Cook Tested-by: Kees Cook Cc: Heiko Carstens Cc: Michael Ellerman Cc: Ingo Molnar Cc: H. Peter Anvin Cc: Benjamin Herrenschmidt Cc: Michal Marek Cc: Rusty Russell Cc: Arnd Bergmann Signed-off-by: Andrew Morton --- init/Kconfig | 16 ++++ kernel/kallsyms.c | 38 +++++++-- scripts/kallsyms.c | 88 +++++++++++++++++--- scripts/link-vmlinux.sh | 4 + scripts/namespace.pl | 2 + 5 files changed, 129 insertions(+), 19 deletions(-) -- 2.5.0 diff --git a/init/Kconfig b/init/Kconfig index 22320804fbaf..1cc72a068afc 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1420,6 +1420,22 @@ config KALLSYMS_ALL Say N unless you really need all symbols. +config KALLSYMS_BASE_RELATIVE + bool + depends on KALLSYMS + default !IA64 + help + Instead of emitting them as absolute values in the native word size, + emit the symbol references in the kallsyms table as 32-bit entries, + each containing either an absolute value in the range [0, S32_MAX] or + a relative value in the range [base, base + S32_MAX], where base is + the lowest relative symbol address encountered in the image. + + On 64-bit builds, this reduces the size of the address table by 50%, + but more importantly, it results in entries whose values are build + time constants, and no relocation pass is required at runtime to fix + up the entries based on the runtime load address of the kernel. + config PRINTK default y bool "Enable support for printk" if EXPERT diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 5c5987f10819..10a8af9d5744 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -38,6 +38,7 @@ * during the second link stage. */ extern const unsigned long kallsyms_addresses[] __weak; +extern const int kallsyms_offsets[] __weak; extern const u8 kallsyms_names[] __weak; /* @@ -47,6 +48,9 @@ extern const u8 kallsyms_names[] __weak; extern const unsigned long kallsyms_num_syms __attribute__((weak, section(".rodata"))); +extern const unsigned long kallsyms_relative_base +__attribute__((weak, section(".rodata"))); + extern const u8 kallsyms_token_table[] __weak; extern const u16 kallsyms_token_index[] __weak; @@ -176,6 +180,19 @@ static unsigned int get_symbol_offset(unsigned long pos) return name - kallsyms_names; } +static unsigned long kallsyms_sym_address(int idx) +{ + if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE)) + return kallsyms_addresses[idx]; + + /* positive offsets are absolute values */ + if (kallsyms_offsets[idx] >= 0) + return kallsyms_offsets[idx]; + + /* negative offsets are relative to kallsyms_relative_base - 1 */ + return kallsyms_relative_base - 1 - kallsyms_offsets[idx]; +} + /* Lookup the address for this symbol. Returns 0 if not found. */ unsigned long kallsyms_lookup_name(const char *name) { @@ -187,7 +204,7 @@ unsigned long kallsyms_lookup_name(const char *name) off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); if (strcmp(namebuf, name) == 0) - return kallsyms_addresses[i]; + return kallsyms_sym_address(i); } return module_kallsyms_lookup_name(name); } @@ -204,7 +221,7 @@ int kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *, for (i = 0, off = 0; i < kallsyms_num_syms; i++) { off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); - ret = fn(data, namebuf, NULL, kallsyms_addresses[i]); + ret = fn(data, namebuf, NULL, kallsyms_sym_address(i)); if (ret != 0) return ret; } @@ -220,7 +237,10 @@ static unsigned long get_symbol_pos(unsigned long addr, unsigned long i, low, high, mid; /* This kernel should never had been booted. */ - BUG_ON(!kallsyms_addresses); + if (!IS_ENABLED(CONFIG_KALLSYMS_BASE_RELATIVE)) + BUG_ON(!kallsyms_addresses); + else + BUG_ON(!kallsyms_offsets); /* Do a binary search on the sorted kallsyms_addresses array. */ low = 0; @@ -228,7 +248,7 @@ static unsigned long get_symbol_pos(unsigned long addr, while (high - low > 1) { mid = low + (high - low) / 2; - if (kallsyms_addresses[mid] <= addr) + if (kallsyms_sym_address(mid) <= addr) low = mid; else high = mid; @@ -238,15 +258,15 @@ static unsigned long get_symbol_pos(unsigned long addr, * Search for the first aliased symbol. Aliased * symbols are symbols with the same address. */ - while (low && kallsyms_addresses[low-1] == kallsyms_addresses[low]) + while (low && kallsyms_sym_address(low-1) == kallsyms_sym_address(low)) --low; - symbol_start = kallsyms_addresses[low]; + symbol_start = kallsyms_sym_address(low); /* Search for next non-aliased symbol. */ for (i = low + 1; i < kallsyms_num_syms; i++) { - if (kallsyms_addresses[i] > symbol_start) { - symbol_end = kallsyms_addresses[i]; + if (kallsyms_sym_address(i) > symbol_start) { + symbol_end = kallsyms_sym_address(i); break; } } @@ -470,7 +490,7 @@ static unsigned long get_ksymbol_core(struct kallsym_iter *iter) unsigned off = iter->nameoff; iter->module_name[0] = '\0'; - iter->value = kallsyms_addresses[iter->pos]; + iter->value = kallsyms_sym_address(iter->pos); iter->type = kallsyms_get_symbol_type(off); diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c index d39a1eeb080e..02473b71643b 100644 --- a/scripts/kallsyms.c +++ b/scripts/kallsyms.c @@ -22,6 +22,7 @@ #include #include #include +#include #ifndef ARRAY_SIZE #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0])) @@ -43,6 +44,7 @@ struct addr_range { }; static unsigned long long _text; +static unsigned long long relative_base; static struct addr_range text_ranges[] = { { "_stext", "_etext" }, { "_sinittext", "_einittext" }, @@ -62,6 +64,7 @@ static int all_symbols = 0; static int absolute_percpu = 0; static char symbol_prefix_char = '\0'; static unsigned long long kernel_start_addr = 0; +static int base_relative = 0; int token_profit[0x10000]; @@ -75,7 +78,7 @@ static void usage(void) fprintf(stderr, "Usage: kallsyms [--all-symbols] " "[--symbol-prefix=] " "[--page-offset=] " - "< in.map > out.S\n"); + "[--base-relative] < in.map > out.S\n"); exit(1); } @@ -205,6 +208,8 @@ static int symbol_valid(struct sym_entry *s) */ static char *special_symbols[] = { "kallsyms_addresses", + "kallsyms_offsets", + "kallsyms_relative_base", "kallsyms_num_syms", "kallsyms_names", "kallsyms_markers", @@ -349,16 +354,47 @@ static void write_src(void) printf("\t.section .rodata, \"a\"\n"); - /* Provide proper symbols relocatability by their '_text' - * relativeness. The symbol names cannot be used to construct - * normal symbol references as the list of symbols contains - * symbols that are declared static and are private to their - * .o files. This prevents .tmp_kallsyms.o or any other - * object from referencing them. + /* Provide proper symbols relocatability by their relativeness + * to a fixed anchor point in the runtime image, either '_text' + * for absolute address tables, in which case the linker will + * emit the final addresses at build time. Otherwise, use the + * offset relative to the lowest value encountered of all relative + * symbols, and emit non-relocatable fixed offsets that will be fixed + * up at runtime. + * + * The symbol names cannot be used to construct normal symbol + * references as the list of symbols contains symbols that are + * declared static and are private to their .o files. This prevents + * .tmp_kallsyms.o or any other object from referencing them. */ - output_label("kallsyms_addresses"); + if (!base_relative) + output_label("kallsyms_addresses"); + else + output_label("kallsyms_offsets"); + for (i = 0; i < table_cnt; i++) { - if (!symbol_absolute(&table[i])) { + if (base_relative) { + long long offset; + + if (symbol_absolute(&table[i])) { + offset = table[i].addr; + if (offset < 0 || offset > INT_MAX) { + fprintf(stderr, "kallsyms failure: " + "absolute symbol value %#llx out of range in relative mode\n", + table[i].addr); + exit(EXIT_FAILURE); + } + } else { + offset = relative_base - table[i].addr - 1; + if (offset < INT_MIN || offset >= 0) { + fprintf(stderr, "kallsyms failure: " + "relative symbol value %#llx out of range in relative mode\n", + table[i].addr); + exit(EXIT_FAILURE); + } + } + printf("\t.long\t%#x\n", (int)offset); + } else if (!symbol_absolute(&table[i])) { if (_text <= table[i].addr) printf("\tPTR\t_text + %#llx\n", table[i].addr - _text); @@ -371,6 +407,12 @@ static void write_src(void) } printf("\n"); + if (base_relative) { + output_label("kallsyms_relative_base"); + printf("\tPTR\t_text - %#llx\n", _text - relative_base); + printf("\n"); + } + output_label("kallsyms_num_syms"); printf("\tPTR\t%d\n", table_cnt); printf("\n"); @@ -695,6 +737,28 @@ static void make_percpus_absolute(void) } } +/* find the minimum non-absolute symbol address */ +static void record_relative_base(void) +{ + unsigned int i; + + if (kernel_start_addr > 0) { + /* + * If the kernel start address was specified, use that as + * the relative base rather than going through the table, + * since it should be a reasonable default, and values below + * it will be ignored anyway. + */ + relative_base = kernel_start_addr; + } else { + relative_base = -1ULL; + for (i = 0; i < table_cnt; i++) + if (!symbol_absolute(&table[i]) && + table[i].addr < relative_base) + relative_base = table[i].addr; + } +} + int main(int argc, char **argv) { if (argc >= 2) { @@ -713,7 +777,9 @@ int main(int argc, char **argv) } else if (strncmp(argv[i], "--page-offset=", 14) == 0) { const char *p = &argv[i][14]; kernel_start_addr = strtoull(p, NULL, 16); - } else + } else if (strcmp(argv[i], "--base-relative") == 0) + base_relative = 1; + else usage(); } } else if (argc != 1) @@ -722,6 +788,8 @@ int main(int argc, char **argv) read_map(stdin); if (absolute_percpu) make_percpus_absolute(); + if (base_relative) + record_relative_base(); sort_symbols(); optimize_token_table(); write_src(); diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh index ba6c34ea5429..b58bf908b153 100755 --- a/scripts/link-vmlinux.sh +++ b/scripts/link-vmlinux.sh @@ -90,6 +90,10 @@ kallsyms() kallsymopt="${kallsymopt} --absolute-percpu" fi + if [ -n "${CONFIG_KALLSYMS_BASE_RELATIVE}" ]; then + kallsymopt="${kallsymopt} --base-relative" + fi + local aflags="${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \ ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS}" diff --git a/scripts/namespace.pl b/scripts/namespace.pl index a71be6b7cdec..9f3c9d47a4a5 100755 --- a/scripts/namespace.pl +++ b/scripts/namespace.pl @@ -117,6 +117,8 @@ my %nameexception = ( 'kallsyms_names' => 1, 'kallsyms_num_syms' => 1, 'kallsyms_addresses'=> 1, + 'kallsyms_offsets' => 1, + 'kallsyms_relative_base'=> 1, '__this_module' => 1, '_etext' => 1, '_edata' => 1,