forked from Minki/linux
2f6c9bf31a
The current VDSO patch mechanism has several problems: 1) It assumes how gcc will emit a function, with a register window, an initial save instruction and then immediately the %tick read when compiling vread_tick(). There is no such guarantees, code generation could change at any time, gcc could put a nop between the save and the %tick read, etc. So this is extremely fragile and would fail some day. 2) It disallows us to properly inline vread_tick() into the callers and thus get the best possible code sequences. So fix this to patch properly, with location based annotations. We have to be careful because we cannot do it the way we do patches elsewhere in the kernel. Those use a sequence like: 1: insn .section .whatever_patch, "ax" .word 1b replacement_insn .previous This is a dynamic shared object, so that .word cannot be resolved at build time, and thus cannot be used to execute the patches when the kernel initializes the images. Even trying to use label difference equations doesn't work in the above kind of scheme: 1: insn .section .whatever_patch, "ax" .word . - 1b replacement_insn .previous The assembler complains that it cannot resolve that computation. The issue is that this is contained in an executable section. Borrow the sequence used by x86 alternatives, which is: 1: insn .pushsection .whatever_patch, "a" .word . - 1b, . - 1f .popsection .pushsection .whatever_patch_replacements, "ax" 1: replacement_insn .previous This works, allows us to inline vread_tick() as much as we like, and can be used for arbitrary kinds of VDSO patching in the future. Also, reverse the condition for patching. Most systems are %stick based, so if we only patch on %tick systems the patching code will get little or no testing. Signed-off-by: David S. Miller <davem@davemloft.net>
158 lines
4.6 KiB
C
158 lines
4.6 KiB
C
/*
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* Copyright (c) 2017 Oracle and/or its affiliates. All rights reserved.
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*/
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/*
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* This file is included up to twice from vdso2c.c. It generates code for
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* 32-bit and 64-bit vDSOs. We will eventually need both for 64-bit builds,
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* since 32-bit vDSOs will then be built for 32-bit userspace.
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*/
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static void BITSFUNC(go)(void *raw_addr, size_t raw_len,
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void *stripped_addr, size_t stripped_len,
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FILE *outfile, const char *name)
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{
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int found_load = 0;
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unsigned long load_size = -1; /* Work around bogus warning */
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unsigned long mapping_size;
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int i;
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unsigned long j;
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ELF(Shdr) *symtab_hdr = NULL, *strtab_hdr, *secstrings_hdr,
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*patch_sec = NULL;
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ELF(Ehdr) *hdr = (ELF(Ehdr) *)raw_addr;
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ELF(Dyn) *dyn = 0, *dyn_end = 0;
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const char *secstrings;
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INT_BITS syms[NSYMS] = {};
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ELF(Phdr) *pt = (ELF(Phdr) *)(raw_addr + GET_BE(&hdr->e_phoff));
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/* Walk the segment table. */
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for (i = 0; i < GET_BE(&hdr->e_phnum); i++) {
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if (GET_BE(&pt[i].p_type) == PT_LOAD) {
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if (found_load)
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fail("multiple PT_LOAD segs\n");
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if (GET_BE(&pt[i].p_offset) != 0 ||
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GET_BE(&pt[i].p_vaddr) != 0)
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fail("PT_LOAD in wrong place\n");
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if (GET_BE(&pt[i].p_memsz) != GET_BE(&pt[i].p_filesz))
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fail("cannot handle memsz != filesz\n");
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load_size = GET_BE(&pt[i].p_memsz);
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found_load = 1;
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} else if (GET_BE(&pt[i].p_type) == PT_DYNAMIC) {
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dyn = raw_addr + GET_BE(&pt[i].p_offset);
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dyn_end = raw_addr + GET_BE(&pt[i].p_offset) +
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GET_BE(&pt[i].p_memsz);
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}
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}
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if (!found_load)
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fail("no PT_LOAD seg\n");
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if (stripped_len < load_size)
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fail("stripped input is too short\n");
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/* Walk the dynamic table */
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for (i = 0; dyn + i < dyn_end &&
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GET_BE(&dyn[i].d_tag) != DT_NULL; i++) {
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typeof(dyn[i].d_tag) tag = GET_BE(&dyn[i].d_tag);
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typeof(dyn[i].d_un.d_val) val = GET_BE(&dyn[i].d_un.d_val);
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if ((tag == DT_RELSZ || tag == DT_RELASZ) && (val != 0))
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fail("vdso image contains dynamic relocations\n");
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}
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/* Walk the section table */
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secstrings_hdr = raw_addr + GET_BE(&hdr->e_shoff) +
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GET_BE(&hdr->e_shentsize)*GET_BE(&hdr->e_shstrndx);
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secstrings = raw_addr + GET_BE(&secstrings_hdr->sh_offset);
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for (i = 0; i < GET_BE(&hdr->e_shnum); i++) {
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ELF(Shdr) *sh = raw_addr + GET_BE(&hdr->e_shoff) +
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GET_BE(&hdr->e_shentsize) * i;
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if (GET_BE(&sh->sh_type) == SHT_SYMTAB)
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symtab_hdr = sh;
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if (!strcmp(secstrings + GET_BE(&sh->sh_name),
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".tick_patch"))
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patch_sec = sh;
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}
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if (!symtab_hdr)
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fail("no symbol table\n");
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strtab_hdr = raw_addr + GET_BE(&hdr->e_shoff) +
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GET_BE(&hdr->e_shentsize) * GET_BE(&symtab_hdr->sh_link);
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/* Walk the symbol table */
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for (i = 0;
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i < GET_BE(&symtab_hdr->sh_size) / GET_BE(&symtab_hdr->sh_entsize);
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i++) {
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int k;
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ELF(Sym) *sym = raw_addr + GET_BE(&symtab_hdr->sh_offset) +
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GET_BE(&symtab_hdr->sh_entsize) * i;
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const char *name = raw_addr + GET_BE(&strtab_hdr->sh_offset) +
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GET_BE(&sym->st_name);
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for (k = 0; k < NSYMS; k++) {
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if (!strcmp(name, required_syms[k].name)) {
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if (syms[k]) {
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fail("duplicate symbol %s\n",
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required_syms[k].name);
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}
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/*
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* Careful: we use negative addresses, but
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* st_value is unsigned, so we rely
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* on syms[k] being a signed type of the
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* correct width.
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*/
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syms[k] = GET_BE(&sym->st_value);
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}
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}
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}
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/* Validate mapping addresses. */
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if (syms[sym_vvar_start] % 8192)
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fail("vvar_begin must be a multiple of 8192\n");
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if (!name) {
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fwrite(stripped_addr, stripped_len, 1, outfile);
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return;
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}
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mapping_size = (stripped_len + 8191) / 8192 * 8192;
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fprintf(outfile, "/* AUTOMATICALLY GENERATED -- DO NOT EDIT */\n\n");
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fprintf(outfile, "#include <linux/cache.h>\n");
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fprintf(outfile, "#include <asm/vdso.h>\n");
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fprintf(outfile, "\n");
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fprintf(outfile,
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"static unsigned char raw_data[%lu] __ro_after_init __aligned(8192)= {",
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mapping_size);
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for (j = 0; j < stripped_len; j++) {
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if (j % 10 == 0)
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fprintf(outfile, "\n\t");
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fprintf(outfile, "0x%02X, ",
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(int)((unsigned char *)stripped_addr)[j]);
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}
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fprintf(outfile, "\n};\n\n");
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fprintf(outfile, "const struct vdso_image %s_builtin = {\n", name);
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fprintf(outfile, "\t.data = raw_data,\n");
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fprintf(outfile, "\t.size = %lu,\n", mapping_size);
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if (patch_sec) {
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fprintf(outfile, "\t.tick_patch = %lu,\n",
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(unsigned long)GET_BE(&patch_sec->sh_offset));
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fprintf(outfile, "\t.tick_patch_len = %lu,\n",
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(unsigned long)GET_BE(&patch_sec->sh_size));
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}
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for (i = 0; i < NSYMS; i++) {
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if (required_syms[i].export && syms[i])
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fprintf(outfile, "\t.sym_%s = %" PRIi64 ",\n",
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required_syms[i].name, (int64_t)syms[i]);
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}
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fprintf(outfile, "};\n");
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}
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