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Message-Id: <d25c7644249355785365914398bdba1ed2c52468.1682673543.git.houwenlong.hwl@antgroup.com>
Date: Fri, 28 Apr 2023 17:51:07 +0800
From: "Hou Wenlong" <houwenlong.hwl@...group.com>
To: linux-kernel@...r.kernel.org
Cc: "Thomas Garnier" <thgarnie@...omium.org>,
"Lai Jiangshan" <jiangshan.ljs@...group.com>,
"Kees Cook" <keescook@...omium.org>,
"Hou Wenlong" <houwenlong.hwl@...group.com>,
"Thomas Gleixner" <tglx@...utronix.de>,
"Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
"Dave Hansen" <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
"H. Peter Anvin" <hpa@...or.com>,
"Sami Tolvanen" <samitolvanen@...gle.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [PATCH RFC 27/43] x86/relocs: Handle PIE relocations
From: Thomas Garnier <thgarnie@...omium.org>
From: Thomas Garnier <thgarnie@...omium.org>
Change the relocation tool to correctly handle relocations generated by
-fPIE option:
- Add relocation for each entry of the .got section given the linker
does not generate R_X86_64_GLOB_DAT on a simple link.
- Ignore R_X86_64_GOTPCREL.
Signed-off-by: Thomas Garnier <thgarnie@...omium.org>
Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
Cc: Lai Jiangshan <jiangshan.ljs@...group.com>
Cc: Kees Cook <keescook@...omium.org>
---
arch/x86/tools/relocs.c | 96 ++++++++++++++++++++++++++++++++++++++++-
1 file changed, 95 insertions(+), 1 deletion(-)
diff --git a/arch/x86/tools/relocs.c b/arch/x86/tools/relocs.c
index 038e9c12fad3..97ac96195232 100644
--- a/arch/x86/tools/relocs.c
+++ b/arch/x86/tools/relocs.c
@@ -42,6 +42,7 @@ struct section {
Elf32_Word *xsymtab;
Elf_Rel *reltab;
char *strtab;
+ Elf_Addr *got;
};
static struct section *secs;
@@ -308,6 +309,36 @@ static Elf_Sym *sym_lookup(const char *symname)
return 0;
}
+static Elf_Sym *sym_lookup_addr(Elf_Addr addr, const char **name)
+{
+ int i;
+
+ for (i = 0; i < ehdr.e_shnum; i++) {
+ struct section *sec = &secs[i];
+ long nsyms;
+ Elf_Sym *symtab;
+ Elf_Sym *sym;
+
+ if (sec->shdr.sh_type != SHT_SYMTAB)
+ continue;
+
+ nsyms = sec->shdr.sh_size/sizeof(Elf_Sym);
+ symtab = sec->symtab;
+
+ for (sym = symtab; --nsyms >= 0; sym++) {
+ if (sym->st_value == addr) {
+ if (name) {
+ *name = sym_name(sec->link->strtab,
+ sym);
+ }
+ return sym;
+ }
+ }
+ }
+ return 0;
+}
+
+
#if BYTE_ORDER == LITTLE_ENDIAN
#define le16_to_cpu(val) (val)
#define le32_to_cpu(val) (val)
@@ -588,6 +619,35 @@ static void read_relocs(FILE *fp)
}
}
+static void read_got(FILE *fp)
+{
+ int i;
+
+ for (i = 0; i < ehdr.e_shnum; i++) {
+ struct section *sec = &secs[i];
+
+ sec->got = NULL;
+ if (sec->shdr.sh_type != SHT_PROGBITS ||
+ strcmp(sec_name(i), ".got")) {
+ continue;
+ }
+ sec->got = malloc(sec->shdr.sh_size);
+ if (!sec->got) {
+ die("malloc of %" FMT " bytes for got failed\n",
+ sec->shdr.sh_size);
+ }
+ if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0) {
+ die("Seek to %" FMT " failed: %s\n",
+ sec->shdr.sh_offset, strerror(errno));
+ }
+ if (fread(sec->got, 1, sec->shdr.sh_size, fp)
+ != sec->shdr.sh_size) {
+ die("Cannot read got: %s\n",
+ strerror(errno));
+ }
+ }
+}
+
static void print_absolute_symbols(void)
{
@@ -718,6 +778,32 @@ static void add_reloc(struct relocs *r, uint32_t offset)
r->offset[r->count++] = offset;
}
+/*
+ * The linker does not generate relocations for the GOT for the kernel.
+ * If a GOT is found, simulate the relocations that should have been included.
+ */
+static void walk_got_table(int (*process)(struct section *sec, Elf_Rel *rel,
+ Elf_Sym *sym, const char *symname),
+ struct section *sec)
+{
+ int i;
+ Elf_Addr entry;
+ Elf_Sym *sym;
+ const char *symname;
+ Elf_Rel rel;
+
+ for (i = 0; i < sec->shdr.sh_size/sizeof(Elf_Addr); i++) {
+ entry = sec->got[i];
+ sym = sym_lookup_addr(entry, &symname);
+ if (!sym)
+ die("Could not found got symbol for entry %d\n", i);
+ rel.r_offset = sec->shdr.sh_addr + i * sizeof(Elf_Addr);
+ rel.r_info = ELF_BITS == 64 ? R_X86_64_GLOB_DAT
+ : R_386_GLOB_DAT;
+ process(sec, &rel, sym, symname);
+ }
+}
+
static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
Elf_Sym *sym, const char *symname))
{
@@ -731,6 +817,8 @@ static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
struct section *sec = &secs[i];
if (sec->shdr.sh_type != SHT_REL_TYPE) {
+ if (sec->got)
+ walk_got_table(process, sec);
continue;
}
sec_symtab = sec->link;
@@ -842,6 +930,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
offset += per_cpu_load_addr;
switch (r_type) {
+ case R_X86_64_GOTPCREL:
case R_X86_64_NONE:
/* NONE can be ignored. */
break;
@@ -905,7 +994,7 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
* the relocations are processed.
* Make sure that the offset will fit.
*/
- if ((int32_t)offset != (int64_t)offset)
+ if (r_type != R_X86_64_64 && (int32_t)offset != (int64_t)offset)
die("Relocation offset doesn't fit in 32 bits\n");
if (r_type == R_X86_64_64)
@@ -914,6 +1003,10 @@ static int do_reloc64(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
add_reloc(&relocs32, offset);
break;
+ case R_X86_64_GLOB_DAT:
+ add_reloc(&relocs64, offset);
+ break;
+
default:
die("Unsupported relocation type: %s (%d)\n",
rel_type(r_type), r_type);
@@ -1188,6 +1281,7 @@ void process(FILE *fp, int use_real_mode, int as_text,
read_strtabs(fp);
read_symtabs(fp);
read_relocs(fp);
+ read_got(fp);
if (ELF_BITS == 64)
percpu_init();
if (show_absolute_syms) {
--
2.31.1
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