x86, vdso: Get rid of the fake section mechanism (da861e18) · Commits · 戴 / test

arch/x86/vdso/Makefile

+10 −6

Original line number	Diff line number	Diff line
		@@ -10,7 +10,7 @@ VDSO32-$(CONFIG_X86_32) := y
		VDSO32-$(CONFIG_COMPAT) := y

		# files to link into the vdso
		vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o vdso-fakesections.o
		vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o

		# files to link into kernel
		obj-y += vma.o
		@@ -37,7 +37,8 @@ vdso_img_sodbg := $(vdso_img-y:%=vdso%.so.dbg)
		obj-y += $(vdso_img_objs)
		targets += $(vdso_img_cfiles)
		targets += $(vdso_img_sodbg)
		.SECONDARY: $(vdso_img-y:%=$(obj)/vdso-image-%.c)
		.SECONDARY: $(vdso_img-y:%=$(obj)/vdso-image-%.c) \
		$(vdso_img-y:%=$(obj)/vdso%.so)

		export CPPFLAGS_vdso.lds += -P -C

		@@ -54,10 +55,10 @@ hostprogs-y += vdso2c

		quiet_cmd_vdso2c = VDSO2C $@
		define cmd_vdso2c
		$(obj)/vdso2c $< $@
		$(obj)/vdso2c $< $(<:%.dbg=%) $@
		endef

		$(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso2c FORCE
		$(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE
		$(call if_changed,vdso2c)

		#
		@@ -113,6 +114,10 @@ $(obj)/%-x32.o: $(obj)/%.o FORCE

		targets += vdsox32.lds $(vobjx32s-y)

		$(obj)/%.so: OBJCOPYFLAGS := -S
		$(obj)/%.so: $(obj)/%.so.dbg
		$(call if_changed,objcopy)

		$(obj)/vdsox32.so.dbg: $(src)/vdsox32.lds $(vobjx32s) FORCE
		$(call if_changed,vdso)

		@@ -134,7 +139,7 @@ override obj-dirs = $(dir $(obj)) $(obj)/vdso32/

		targets += vdso32/vdso32.lds
		targets += vdso32/note.o vdso32/vclock_gettime.o $(vdso32.so-y:%=vdso32/%.o)
		targets += vdso32/vclock_gettime.o vdso32/vdso-fakesections.o
		targets += vdso32/vclock_gettime.o

		$(obj)/vdso32.o: $(vdso32-images:%=$(obj)/%)

		@@ -156,7 +161,6 @@ $(vdso32-images:%=$(obj)/%.dbg): KBUILD_CFLAGS = $(KBUILD_CFLAGS_32)
		$(vdso32-images:%=$(obj)/%.dbg): $(obj)/vdso32-%.so.dbg: FORCE \
		$(obj)/vdso32/vdso32.lds \
		$(obj)/vdso32/vclock_gettime.o \
		$(obj)/vdso32/vdso-fakesections.o \
		$(obj)/vdso32/note.o \
		$(obj)/vdso32/%.o
		$(call if_changed,vdso)

arch/x86/vdso/vdso-fakesections.c

deleted100644 → 0

+0 −21

Original line number	Diff line number	Diff line
		/*
		* Copyright 2014 Andy Lutomirski
		* Subject to the GNU Public License, v.2
		*
		* String table for loadable section headers. See vdso2c.h for why
		* this exists.
		*/

		const char fake_shstrtab[] __attribute__((section(".fake_shstrtab"))) =
		".hash\0"
		".dynsym\0"
		".dynstr\0"
		".gnu.version\0"
		".gnu.version_d\0"
		".dynamic\0"
		".rodata\0"
		".fake_shstrtab\0" /* Yay, self-referential code. */
		".note\0"
		".eh_frame_hdr\0"
		".eh_frame\0"
		".text";

arch/x86/vdso/vdso2c.c

+91 −25

Original line number	Diff line number	Diff line
		/*
		* vdso2c - A vdso image preparation tool
		* Copyright (c) 2014 Andy Lutomirski and others
		* Licensed under the GPL v2
		*
		* vdso2c requires stripped and unstripped input. It would be trivial
		* to fully strip the input in here, but, for reasons described below,
		* we need to write a section table. Doing this is more or less
		* equivalent to dropping all non-allocatable sections, but it's
		* easier to let objcopy handle that instead of doing it ourselves.
		* If we ever need to do something fancier than what objcopy provides,
		* it would be straightforward to add here.
		*
		* We're keep a section table for a few reasons:
		*
		* The Go runtime had a couple of bugs: it would read the section
		* table to try to figure out how many dynamic symbols there were (it
		* shouldn't have looked at the section table at all) and, if there
		* were no SHT_SYNDYM section table entry, it would use an
		* uninitialized value for the number of symbols. An empty DYNSYM
		* table would work, but I see no reason not to write a valid one (and
		* keep full performance for old Go programs). This hack is only
		* needed on x86_64.
		*
		* The bug was introduced on 2012-08-31 by:
		* https://code.google.com/p/go/source/detail?r=56ea40aac72b
		* and was fixed on 2014-06-13 by:
		* https://code.google.com/p/go/source/detail?r=fc1cd5e12595
		*
		* Binutils has issues debugging the vDSO: it reads the section table to
		* find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
		* would break build-id if we removed the section table. Binutils
		* also requires that shstrndx != 0. See:
		* https://sourceware.org/bugzilla/show_bug.cgi?id=17064
		*
		* elfutils might not look for PT_NOTE if there is a section table at
		* all. I don't know whether this matters for any practical purpose.
		*
		* For simplicity, rather than hacking up a partial section table, we
		* just write a mostly complete one. We omit non-dynamic symbols,
		* though, since they're rather large.
		*
		* Once binutils gets fixed, we might be able to drop this for all but
		* the 64-bit vdso, since build-id only works in kernel RPMs, and
		* systems that update to new enough kernel RPMs will likely update
		* binutils in sync. build-id has never worked for home-built kernel
		* RPMs without manual symlinking, and I suspect that no one ever does
		* that.
		*/

		#include <inttypes.h>
		#include <stdint.h>
		#include <unistd.h>
		@@ -61,6 +111,7 @@ static void fail(const char *format, ...)
		va_start(ap, format);
		fprintf(stderr, "Error: ");
		vfprintf(stderr, format, ap);
		if (outfilename)
		unlink(outfilename);
		exit(1);
		va_end(ap);
		@@ -114,30 +165,53 @@ extern void bad_put_le(void);
		#include "vdso2c.h"
		#undef ELF_BITS

		static void go(void addr, size_t len, FILE outfile, const char *name)
		static void go(void *raw_addr, size_t raw_len,
		void *stripped_addr, size_t stripped_len,
		FILE outfile, const char name)
		{
		Elf64_Ehdr hdr = (Elf64_Ehdr )addr;
		Elf64_Ehdr hdr = (Elf64_Ehdr )raw_addr;

		if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
		go64(addr, len, outfile, name);
		go64(raw_addr, raw_len, stripped_addr, stripped_len,
		outfile, name);
		} else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
		go32(addr, len, outfile, name);
		go32(raw_addr, raw_len, stripped_addr, stripped_len,
		outfile, name);
		} else {
		fail("unknown ELF class\n");
		}
		}

		static void map_input(const char name, void addr, size_t len, int prot)
		{
		off_t tmp_len;

		int fd = open(name, O_RDONLY);
		if (fd == -1)
		err(1, "%s", name);

		tmp_len = lseek(fd, 0, SEEK_END);
		if (tmp_len == (off_t)-1)
		err(1, "lseek");
		*len = (size_t)tmp_len;

		*addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
		if (*addr == MAP_FAILED)
		err(1, "mmap");

		close(fd);
		}

		int main(int argc, char **argv)
		{
		int fd;
		off_t len;
		void *addr;
		size_t raw_len, stripped_len;
		void raw_addr, stripped_addr;
		FILE *outfile;
		char name, tmp;
		int namelen;

		if (argc != 3) {
		printf("Usage: vdso2c INPUT OUTPUT\n");
		if (argc != 4) {
		printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
		return 1;
		}

		@@ -145,7 +219,7 @@ int main(int argc, char **argv)
		* Figure out the struct name. If we're writing to a .so file,
		* generate raw output insted.
		*/
		name = strdup(argv[2]);
		name = strdup(argv[3]);
		namelen = strlen(name);
		if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
		name = NULL;
		@@ -161,26 +235,18 @@ int main(int argc, char **argv)
		*tmp = '_';
		}

		fd = open(argv[1], O_RDONLY);
		if (fd == -1)
		err(1, "%s", argv[1]);

		len = lseek(fd, 0, SEEK_END);
		if (len == (off_t)-1)
		err(1, "lseek");

		addr = mmap(NULL, len, PROT_READ \| PROT_WRITE, MAP_PRIVATE, fd, 0);
		if (addr == MAP_FAILED)
		err(1, "mmap");
		map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
		map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);

		outfilename = argv[2];
		outfilename = argv[3];
		outfile = fopen(outfilename, "w");
		if (!outfile)
		err(1, "%s", argv[2]);

		go(addr, (size_t)len, outfile, name);
		go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);

		munmap(addr, len);
		munmap(raw_addr, raw_len);
		munmap(stripped_addr, stripped_len);
		fclose(outfile);

		return 0;

arch/x86/vdso/vdso2c.h

+25 −177

Original line number	Diff line number	Diff line
		@@ -4,128 +4,14 @@
		* are built for 32-bit userspace.
		*/

		/*
		* We're writing a section table for a few reasons:
		*
		* The Go runtime had a couple of bugs: it would read the section
		* table to try to figure out how many dynamic symbols there were (it
		* shouldn't have looked at the section table at all) and, if there
		* were no SHT_SYNDYM section table entry, it would use an
		* uninitialized value for the number of symbols. An empty DYNSYM
		* table would work, but I see no reason not to write a valid one (and
		* keep full performance for old Go programs). This hack is only
		* needed on x86_64.
		*
		* The bug was introduced on 2012-08-31 by:
		* https://code.google.com/p/go/source/detail?r=56ea40aac72b
		* and was fixed on 2014-06-13 by:
		* https://code.google.com/p/go/source/detail?r=fc1cd5e12595
		*
		* Binutils has issues debugging the vDSO: it reads the section table to
		* find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
		* would break build-id if we removed the section table. Binutils
		* also requires that shstrndx != 0. See:
		* https://sourceware.org/bugzilla/show_bug.cgi?id=17064
		*
		* elfutils might not look for PT_NOTE if there is a section table at
		* all. I don't know whether this matters for any practical purpose.
		*
		* For simplicity, rather than hacking up a partial section table, we
		* just write a mostly complete one. We omit non-dynamic symbols,
		* though, since they're rather large.
		*
		* Once binutils gets fixed, we might be able to drop this for all but
		* the 64-bit vdso, since build-id only works in kernel RPMs, and
		* systems that update to new enough kernel RPMs will likely update
		* binutils in sync. build-id has never worked for home-built kernel
		* RPMs without manual symlinking, and I suspect that no one ever does
		* that.
		*/
		struct BITSFUNC(fake_sections)
		{
		ELF(Shdr) *table;
		unsigned long table_offset;
		int count, max_count;

		int in_shstrndx;
		unsigned long shstr_offset;
		const char *shstrtab;
		size_t shstrtab_len;

		int out_shstrndx;
		};

		static unsigned int BITSFUNC(find_shname)(struct BITSFUNC(fake_sections) *out,
		const char *name)
		{
		const char *outname = out->shstrtab;
		while (outname - out->shstrtab < out->shstrtab_len) {
		if (!strcmp(name, outname))
		return (outname - out->shstrtab) + out->shstr_offset;
		outname += strlen(outname) + 1;
		}

		if (*name)
		printf("Warning: could not find output name \"%s\"\n", name);
		return out->shstr_offset + out->shstrtab_len - 1; /* Use a null. */
		}

		static void BITSFUNC(init_sections)(struct BITSFUNC(fake_sections) *out)
		{
		if (!out->in_shstrndx)
		fail("didn't find the fake shstrndx\n");

		memset(out->table, 0, out->max_count * sizeof(ELF(Shdr)));

		if (out->max_count < 1)
		fail("we need at least two fake output sections\n");

		PUT_LE(&out->table[0].sh_type, SHT_NULL);
		PUT_LE(&out->table[0].sh_name, BITSFUNC(find_shname)(out, ""));

		out->count = 1;
		}

		static void BITSFUNC(copy_section)(struct BITSFUNC(fake_sections) *out,
		int in_idx, const ELF(Shdr) *in,
		const char *name)
		{
		uint64_t flags = GET_LE(&in->sh_flags);

		bool copy = flags & SHF_ALLOC &&
		(GET_LE(&in->sh_size) \|\|
		(GET_LE(&in->sh_type) != SHT_RELA &&
		GET_LE(&in->sh_type) != SHT_REL)) &&
		strcmp(name, ".altinstructions") &&
		strcmp(name, ".altinstr_replacement");

		if (!copy)
		return;

		if (out->count >= out->max_count)
		fail("too many copied sections (max = %d)\n", out->max_count);

		if (in_idx == out->in_shstrndx)
		out->out_shstrndx = out->count;

		out->table[out->count] = *in;
		PUT_LE(&out->table[out->count].sh_name,
		BITSFUNC(find_shname)(out, name));

		/* elfutils requires that a strtab have the correct type. */
		if (!strcmp(name, ".fake_shstrtab"))
		PUT_LE(&out->table[out->count].sh_type, SHT_STRTAB);

		out->count++;
		}

		static void BITSFUNC(go)(void *addr, size_t len,
		static void BITSFUNC(go)(void *raw_addr, size_t raw_len,
		void *stripped_addr, size_t stripped_len,
		FILE outfile, const char name)
		{
		int found_load = 0;
		unsigned long load_size = -1; /* Work around bogus warning */
		unsigned long data_size;
		ELF(Ehdr) hdr = (ELF(Ehdr) )addr;
		unsigned long mapping_size;
		ELF(Ehdr) hdr = (ELF(Ehdr) )raw_addr;
		int i;
		unsigned long j;
		ELF(Shdr) symtab_hdr = NULL, strtab_hdr, *secstrings_hdr,
		@@ -134,9 +20,7 @@ static void BITSFUNC(go)(void *addr, size_t len,
		const char *secstrings;
		INT_BITS syms[NSYMS] = {};

		struct BITSFUNC(fake_sections) fake_sections = {};

		ELF(Phdr) pt = (ELF(Phdr) )(addr + GET_LE(&hdr->e_phoff));
		ELF(Phdr) pt = (ELF(Phdr) )(raw_addr + GET_LE(&hdr->e_phoff));

		/* Walk the segment table. */
		for (i = 0; i < GET_LE(&hdr->e_phnum); i++) {
		@@ -154,14 +38,16 @@ static void BITSFUNC(go)(void *addr, size_t len,
		load_size = GET_LE(&pt[i].p_memsz);
		found_load = 1;
		} else if (GET_LE(&pt[i].p_type) == PT_DYNAMIC) {
		dyn = addr + GET_LE(&pt[i].p_offset);
		dyn_end = addr + GET_LE(&pt[i].p_offset) +
		dyn = raw_addr + GET_LE(&pt[i].p_offset);
		dyn_end = raw_addr + GET_LE(&pt[i].p_offset) +
		GET_LE(&pt[i].p_memsz);
		}
		}
		if (!found_load)
		fail("no PT_LOAD seg\n");
		data_size = (load_size + 4095) / 4096 * 4096;

		if (stripped_len < load_size)
		fail("stripped input is too short\n");

		/* Walk the dynamic table */
		for (i = 0; dyn + i < dyn_end &&
		@@ -173,11 +59,11 @@ static void BITSFUNC(go)(void *addr, size_t len,
		}

		/* Walk the section table */
		secstrings_hdr = addr + GET_LE(&hdr->e_shoff) +
		secstrings_hdr = raw_addr + GET_LE(&hdr->e_shoff) +
		GET_LE(&hdr->e_shentsize)*GET_LE(&hdr->e_shstrndx);
		secstrings = addr + GET_LE(&secstrings_hdr->sh_offset);
		secstrings = raw_addr + GET_LE(&secstrings_hdr->sh_offset);
		for (i = 0; i < GET_LE(&hdr->e_shnum); i++) {
		ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) +
		ELF(Shdr) *sh = raw_addr + GET_LE(&hdr->e_shoff) +
		GET_LE(&hdr->e_shentsize) * i;
		if (GET_LE(&sh->sh_type) == SHT_SYMTAB)
		symtab_hdr = sh;
		@@ -190,7 +76,7 @@ static void BITSFUNC(go)(void *addr, size_t len,
		if (!symtab_hdr)
		fail("no symbol table\n");

		strtab_hdr = addr + GET_LE(&hdr->e_shoff) +
		strtab_hdr = raw_addr + GET_LE(&hdr->e_shoff) +
		GET_LE(&hdr->e_shentsize) * GET_LE(&symtab_hdr->sh_link);

		/* Walk the symbol table */
		@@ -198,9 +84,9 @@ static void BITSFUNC(go)(void *addr, size_t len,
		i < GET_LE(&symtab_hdr->sh_size) / GET_LE(&symtab_hdr->sh_entsize);
		i++) {
		int k;
		ELF(Sym) *sym = addr + GET_LE(&symtab_hdr->sh_offset) +
		ELF(Sym) *sym = raw_addr + GET_LE(&symtab_hdr->sh_offset) +
		GET_LE(&symtab_hdr->sh_entsize) * i;
		const char *name = addr + GET_LE(&strtab_hdr->sh_offset) +
		const char *name = raw_addr + GET_LE(&strtab_hdr->sh_offset) +
		GET_LE(&sym->st_name);

		for (k = 0; k < NSYMS; k++) {
		@@ -219,48 +105,7 @@ static void BITSFUNC(go)(void *addr, size_t len,
		syms[k] = GET_LE(&sym->st_value);
		}
		}

		if (!strcmp(name, "fake_shstrtab")) {
		ELF(Shdr) *sh;

		fake_sections.in_shstrndx = GET_LE(&sym->st_shndx);
		fake_sections.shstrtab = addr + GET_LE(&sym->st_value);
		fake_sections.shstrtab_len = GET_LE(&sym->st_size);
		sh = addr + GET_LE(&hdr->e_shoff) +
		GET_LE(&hdr->e_shentsize) *
		fake_sections.in_shstrndx;
		fake_sections.shstr_offset = GET_LE(&sym->st_value) -
		GET_LE(&sh->sh_addr);
		}
		}

		/* Build the output section table. */
		if (!syms[sym_VDSO_FAKE_SECTION_TABLE_START] \|\|
		!syms[sym_VDSO_FAKE_SECTION_TABLE_END])
		fail("couldn't find fake section table\n");
		if ((syms[sym_VDSO_FAKE_SECTION_TABLE_END] -
		syms[sym_VDSO_FAKE_SECTION_TABLE_START]) % sizeof(ELF(Shdr)))
		fail("fake section table size isn't a multiple of sizeof(Shdr)\n");
		fake_sections.table = addr + syms[sym_VDSO_FAKE_SECTION_TABLE_START];
		fake_sections.table_offset = syms[sym_VDSO_FAKE_SECTION_TABLE_START];
		fake_sections.max_count = (syms[sym_VDSO_FAKE_SECTION_TABLE_END] -
		syms[sym_VDSO_FAKE_SECTION_TABLE_START]) /
		sizeof(ELF(Shdr));

		BITSFUNC(init_sections)(&fake_sections);
		for (i = 0; i < GET_LE(&hdr->e_shnum); i++) {
		ELF(Shdr) *sh = addr + GET_LE(&hdr->e_shoff) +
		GET_LE(&hdr->e_shentsize) * i;
		BITSFUNC(copy_section)(&fake_sections, i, sh,
		secstrings + GET_LE(&sh->sh_name));
		}
		if (!fake_sections.out_shstrndx)
		fail("didn't generate shstrndx?!?\n");

		PUT_LE(&hdr->e_shoff, fake_sections.table_offset);
		PUT_LE(&hdr->e_shentsize, sizeof(ELF(Shdr)));
		PUT_LE(&hdr->e_shnum, fake_sections.count);
		PUT_LE(&hdr->e_shstrndx, fake_sections.out_shstrndx);

		/* Validate mapping addresses. */
		for (i = 0; i < sizeof(special_pages) / sizeof(special_pages[0]); i++) {
		@@ -281,10 +126,12 @@ static void BITSFUNC(go)(void *addr, size_t len,
		fail("vvar_begin must be a multiple of 4096\n");

		if (!name) {
		fwrite(addr, load_size, 1, outfile);
		fwrite(stripped_addr, stripped_len, 1, outfile);
		return;
		}

		mapping_size = (stripped_len + 4095) / 4096 * 4096;

		fprintf(outfile, "/* AUTOMATICALLY GENERATED -- DO NOT EDIT */\n\n");
		fprintf(outfile, "#include <linux/linkage.h>\n");
		fprintf(outfile, "#include <asm/page_types.h>\n");
		@@ -292,20 +139,21 @@ static void BITSFUNC(go)(void *addr, size_t len,
		fprintf(outfile, "\n");
		fprintf(outfile,
		"static unsigned char raw_data[%lu] __page_aligned_data = {",
		data_size);
		for (j = 0; j < load_size; j++) {
		mapping_size);
		for (j = 0; j < stripped_len; j++) {
		if (j % 10 == 0)
		fprintf(outfile, "\n\t");
		fprintf(outfile, "0x%02X, ", (int)((unsigned char *)addr)[j]);
		fprintf(outfile, "0x%02X, ",
		(int)((unsigned char *)stripped_addr)[j]);
		}
		fprintf(outfile, "\n};\n\n");

		fprintf(outfile, "static struct page *pages[%lu];\n\n",
		data_size / 4096);
		mapping_size / 4096);

		fprintf(outfile, "const struct vdso_image %s = {\n", name);
		fprintf(outfile, "\t.data = raw_data,\n");
		fprintf(outfile, "\t.size = %lu,\n", data_size);
		fprintf(outfile, "\t.size = %lu,\n", mapping_size);
		fprintf(outfile, "\t.text_mapping = {\n");
		fprintf(outfile, "\t\t.name = \"[vdso]\",\n");
		fprintf(outfile, "\t\t.pages = pages,\n");

Admin message