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Miller" , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , Peter Zijlstra , Josh Poimboeuf , Thomas Garnier , Arnd Bergmann , Matthias Kaehlcke , Boris Ostrovsky , Juergen Gross , Paolo Bonzini , =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= , Joerg Roedel , Andy Lutomirski , Borislav Petkov , "Kirill A . Shutemov" , Brian Gerst , Borislav Petkov , Christian Borntraeger , "Rafael J . Wysocki" , Len Brown , Pavel Machek , Tejun Heo , Christoph Lameter , Kees Cook , Paul Gortmaker , Chris Metcalf , "Paul E . McKenney" , Andrew Morton , Christopher Li , Dou Liyang , Masahiro Yamada , Daniel Borkmann , Markus Trippelsdorf , Peter Foley , Steven Rostedt , Tim Chen , Ard Biesheuvel , Catalin Marinas , Matthew Wilcox , Michal Hocko , Rob Landley , Jiri Kosina , "H . J . Lu" , Paul Bolle , Baoquan He , Daniel Micay Date: Tue, 18 Jul 2017 15:33:29 -0700 Message-Id: <20170718223333.110371-19-thgarnie@google.com> X-Mailer: git-send-email 2.13.2.932.g7449e964c-goog In-Reply-To: <20170718223333.110371-1-thgarnie@google.com> References: <20170718223333.110371-1-thgarnie@google.com> Cc: linux-arch@vger.kernel.org, kvm@vger.kernel.org, linux-pm@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-sparse@vger.kernel.org, linux-crypto@vger.kernel.org, kernel-hardening@lists.openwall.com, xen-devel@lists.xenproject.org Subject: [Xen-devel] [RFC 18/22] x86/relocs: Handle DYN relocations for PIE support X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" X-Virus-Scanned: ClamAV using ClamSMTP Change the relocation tool to correctly handle DYN/PIE kernel where the relocation table does not reference symbols and percpu support is not needed. Also add support for R_X86_64_RELATIVE relocations that can be handled like a 64-bit relocation due to the usage of -Bsymbolic. Position Independent Executable (PIE) support will allow to extended the KASLR randomization range below the -2G memory limit. Signed-off-by: Thomas Garnier --- arch/x86/tools/relocs.c | 74 +++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 65 insertions(+), 9 deletions(-) diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c index 73eb7fd4aec4..70f523dd68ff 100644 --- a/arch/x86/tools/relocs.c +++ b/arch/x86/tools/relocs.c @@ -642,6 +642,13 @@ static void add_reloc(struct relocs *r, uint32_t offset) r->offset[r->count++] = offset; } +/* Relocation found in a DYN binary, support only for 64-bit PIE */ +static int is_dyn_reloc(struct section *sec) +{ + return ELF_BITS == 64 && ehdr.e_type == ET_DYN && + sec->shdr.sh_info == SHT_NULL; +} + static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel, Elf_Sym *sym, const char *symname)) { @@ -652,6 +659,7 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel, Elf_Sym *sh_symtab; struct section *sec_applies, *sec_symtab; int j; + int dyn_reloc = 0; struct section *sec = &secs[i]; if (sec->shdr.sh_type != SHT_REL_TYPE) { @@ -660,14 +668,20 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel, sec_symtab = sec->link; sec_applies = &secs[sec->shdr.sh_info]; if (!(sec_applies->shdr.sh_flags & SHF_ALLOC)) { - continue; + if (!is_dyn_reloc(sec_applies)) + continue; + dyn_reloc = 1; } sh_symtab = sec_symtab->symtab; sym_strtab = sec_symtab->link->strtab; for (j = 0; j < sec->shdr.sh_size/sizeof(Elf_Rel); j++) { Elf_Rel *rel = &sec->reltab[j]; - Elf_Sym *sym = &sh_symtab[ELF_R_SYM(rel->r_info)]; - const char *symname = sym_name(sym_strtab, sym); + Elf_Sym *sym = NULL; + const char *symname = NULL; + if (!dyn_reloc) { + sym = &sh_symtab[ELF_R_SYM(rel->r_info)]; + symname = sym_name(sym_strtab, sym); + } process(sec, rel, sym, symname); } @@ -746,16 +760,21 @@ static int is_percpu_sym(ElfW(Sym) *sym, const char *symname) strncmp(symname, "init_per_cpu_", 13); } - static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, const char *symname) { unsigned r_type = ELF64_R_TYPE(rel->r_info); ElfW(Addr) offset = rel->r_offset; - int shn_abs = (sym->st_shndx == SHN_ABS) && !is_reloc(S_REL, symname); + int shn_abs = 0; + int dyn_reloc = is_dyn_reloc(sec); - if (sym->st_shndx == SHN_UNDEF) - return 0; + if (!dyn_reloc) { + shn_abs = (sym->st_shndx == SHN_ABS) && + !is_reloc(S_REL, symname); + + if (sym->st_shndx == SHN_UNDEF) + return 0; + } /* * Adjust the offset if this reloc applies to the percpu section. @@ -769,6 +788,9 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, break; case R_X86_64_PC32: + if (dyn_reloc) + die("PC32 reloc in PIE DYN binary"); + /* * PC relative relocations don't need to be adjusted unless * referencing a percpu symbol. @@ -783,7 +805,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, /* * References to the percpu area don't need to be adjusted. */ - if (is_percpu_sym(sym, symname)) + if (!dyn_reloc && is_percpu_sym(sym, symname)) break; if (shn_abs) { @@ -814,6 +836,14 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, add_reloc(&relocs32, offset); break; + case R_X86_64_RELATIVE: + /* + * -Bsymbolic means we don't need the addend and we can reuse + * the original relocs64. + */ + add_reloc(&relocs64, offset); + break; + default: die("Unsupported relocation type: %s (%d)\n", rel_type(r_type), r_type); @@ -1044,6 +1074,21 @@ static void emit_relocs(int as_text, int use_real_mode) } } +/* Print a different header based on the type of relocation */ +static void print_reloc_header(struct section *sec) { + static int header_printed = 0; + int header_type = is_dyn_reloc(sec) ? 2 : 1; + + if (header_printed == header_type) + return; + header_printed = header_type; + + if (header_type == 2) + printf("reloc type\toffset\tvalue\n"); + else + printf("reloc section\treloc type\tsymbol\tsymbol section\n"); +} + /* * As an aid to debugging problems with different linkers * print summary information about the relocs. @@ -1053,6 +1098,18 @@ static void emit_relocs(int as_text, int use_real_mode) static int do_reloc_info(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, const char *symname) { + + print_reloc_header(sec); + +#if ELF_BITS == 64 + if (is_dyn_reloc(sec)) { + printf("%s\t0x%lx\t0x%lx\n", + rel_type(ELF_R_TYPE(rel->r_info)), + rel->r_offset, + rel->r_addend); + return 0; + } +#endif printf("%s\t%s\t%s\t%s\n", sec_name(sec->shdr.sh_info), rel_type(ELF_R_TYPE(rel->r_info)), @@ -1063,7 +1120,6 @@ static int do_reloc_info(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym, static void print_reloc_info(void) { - printf("reloc section\treloc type\tsymbol\tsymbol section\n"); walk_relocs(do_reloc_info); }