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SubjectRe: [RFC][PATCH 6/6] objtool,x86: Rewrite retpoline thunk calls
On Sat, Feb 20, 2021 at 06:41:01PM +0100, Borislav Petkov wrote:
> > - I have more cases for objtool to rewrite code (I'll see if I can
> > rebase and post that this weekend -- no promises).
>
> Oh noes.

11 patches and one beer later, it even boots :-)

Saves more than 6k on a defconfig build.

I'll push it out to git in a bit.

--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -4,12 +4,12 @@

#define HAVE_JUMP_LABEL_BATCH

-#define JUMP_LABEL_NOP_SIZE 5
-
#ifdef CONFIG_X86_64
-# define STATIC_KEY_INIT_NOP P6_NOP5_ATOMIC
+# define STATIC_KEY_NOP2 P6_NOP2
+# define STATIC_KEY_NOP5 P6_NOP5_ATOMIC
#else
-# define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC
+# define STATIC_KEY_NOP2 GENERIC_NOP2
+# define STATIC_KEY_NOP5 GENERIC_NOP5_ATOMIC
#endif

#include <asm/asm.h>
@@ -20,15 +20,35 @@
#include <linux/stringify.h>
#include <linux/types.h>

+#define JUMP_TABLE_ENTRY \
+ ".pushsection __jump_table, \"aw\" \n\t" \
+ _ASM_ALIGN "\n\t" \
+ ".long 1b - . \n\t" \
+ ".long %l[l_yes] - . \n\t" \
+ _ASM_PTR "%c0 + %c1 - .\n\t" \
+ ".popsection \n\t"
+
+#ifdef CONFIG_STACK_VALIDATION
+
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
+{
+ asm_volatile_goto("1:"
+ "jmp %l[l_yes] # objtool NOPs this \n\t"
+ JUMP_TABLE_ENTRY
+ : : "i" (key), "i" (2 | branch) : : l_yes);
+
+ return false;
+l_yes:
+ return true;
+}
+
+#else
+
static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
{
asm_volatile_goto("1:"
- ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
- ".pushsection __jump_table, \"aw\" \n\t"
- _ASM_ALIGN "\n\t"
- ".long 1b - ., %l[l_yes] - . \n\t"
- _ASM_PTR "%c0 + %c1 - .\n\t"
- ".popsection \n\t"
+ ".byte " __stringify(STATIC_KEY_NOP5) "\n\t"
+ JUMP_TABLE_ENTRY
: : "i" (key), "i" (branch) : : l_yes);

return false;
@@ -36,16 +56,13 @@ static __always_inline bool arch_static_
return true;
}

+#endif /* STACK_VALIDATION */
+
static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
{
asm_volatile_goto("1:"
- ".byte 0xe9\n\t .long %l[l_yes] - 2f\n\t"
- "2:\n\t"
- ".pushsection __jump_table, \"aw\" \n\t"
- _ASM_ALIGN "\n\t"
- ".long 1b - ., %l[l_yes] - . \n\t"
- _ASM_PTR "%c0 + %c1 - .\n\t"
- ".popsection \n\t"
+ "jmp %l[l_yes]\n\t"
+ JUMP_TABLE_ENTRY
: : "i" (key), "i" (branch) : : l_yes);

return false;
@@ -53,41 +70,7 @@ static __always_inline bool arch_static_
return true;
}

-#else /* __ASSEMBLY__ */
-
-.macro STATIC_JUMP_IF_TRUE target, key, def
-.Lstatic_jump_\@:
- .if \def
- /* Equivalent to "jmp.d32 \target" */
- .byte 0xe9
- .long \target - .Lstatic_jump_after_\@
-.Lstatic_jump_after_\@:
- .else
- .byte STATIC_KEY_INIT_NOP
- .endif
- .pushsection __jump_table, "aw"
- _ASM_ALIGN
- .long .Lstatic_jump_\@ - ., \target - .
- _ASM_PTR \key - .
- .popsection
-.endm
-
-.macro STATIC_JUMP_IF_FALSE target, key, def
-.Lstatic_jump_\@:
- .if \def
- .byte STATIC_KEY_INIT_NOP
- .else
- /* Equivalent to "jmp.d32 \target" */
- .byte 0xe9
- .long \target - .Lstatic_jump_after_\@
-.Lstatic_jump_after_\@:
- .endif
- .pushsection __jump_table, "aw"
- _ASM_ALIGN
- .long .Lstatic_jump_\@ - ., \target - .
- _ASM_PTR \key + 1 - .
- .popsection
-.endm
+extern int arch_jump_entry_size(struct jump_entry *entry);

#endif /* __ASSEMBLY__ */

--- a/arch/x86/include/asm/nops.h
+++ b/arch/x86/include/asm/nops.h
@@ -5,6 +5,7 @@
/*
* Define nops for use with alternative() and for tracing.
*
+ * *_NOP2 must be a single instruction
* *_NOP5_ATOMIC must be a single instruction.
*/

--- a/arch/x86/kernel/jump_label.c
+++ b/arch/x86/kernel/jump_label.c
@@ -16,53 +16,81 @@
#include <asm/alternative.h>
#include <asm/text-patching.h>

-static void bug_at(const void *ip, int line)
+int arch_jump_entry_size(struct jump_entry *entry)
{
- /*
- * The location is not an op that we were expecting.
- * Something went wrong. Crash the box, as something could be
- * corrupting the kernel.
- */
- pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph) %d\n", ip, ip, ip, line);
- BUG();
+ struct insn insn;
+
+ kernel_insn_init(&insn, (void *)jump_entry_code(entry), MAX_INSN_SIZE);
+ insn_get_length(&insn);
+ BUG_ON(insn.length != 2 && insn.length != 5);
+
+ return insn.length;
}

-static const void *
-__jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type, int init)
+struct jump_label_patch {
+ const void *code;
+ int size;
+};
+
+static struct jump_label_patch
+__jump_label_patch(struct jump_entry *entry, enum jump_label_type type, int init)
{
- const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
- const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
- const void *expect, *code;
+ const unsigned char default_nop2[] = { STATIC_KEY_NOP2 };
+ const unsigned char default_nop5[] = { STATIC_KEY_NOP5 };
+ const void *expect, *code, *nop, *default_nop;
const void *addr, *dest;
- int line;
+ int line, size;

addr = (void *)jump_entry_code(entry);
dest = (void *)jump_entry_target(entry);

- code = text_gen_insn(JMP32_INSN_OPCODE, addr, dest);
+ size = arch_jump_entry_size(entry);
+ switch (size) {
+ case JMP8_INSN_SIZE:
+ code = text_gen_insn(JMP8_INSN_OPCODE, addr, dest);
+ default_nop = default_nop2;
+ nop = ideal_nops[2];
+ break;
+
+ case JMP32_INSN_SIZE:
+ code = text_gen_insn(JMP32_INSN_OPCODE, addr, dest);
+ default_nop = default_nop5;
+ nop = ideal_nops[NOP_ATOMIC5];
+ break;
+
+ default: BUG();
+ }

if (init) {
expect = default_nop; line = __LINE__;
} else if (type == JUMP_LABEL_JMP) {
- expect = ideal_nop; line = __LINE__;
+ expect = nop; line = __LINE__;
} else {
expect = code; line = __LINE__;
}

- if (memcmp(addr, expect, JUMP_LABEL_NOP_SIZE))
- bug_at(addr, line);
+ if (memcmp(addr, expect, size)) {
+ /*
+ * The location is not an op that we were expecting.
+ * Something went wrong. Crash the box, as something could be
+ * corrupting the kernel.
+ */
+ pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph != %5ph)) line:%d init:%d size:%d type:%d\n",
+ addr, addr, addr, expect, line, init, size, type);
+ BUG();
+ }

if (type == JUMP_LABEL_NOP)
- code = ideal_nop;
+ code = nop;

- return code;
+ return (struct jump_label_patch){.code = code, .size = size};
}

static inline void __jump_label_transform(struct jump_entry *entry,
enum jump_label_type type,
int init)
{
- const void *opcode = __jump_label_set_jump_code(entry, type, init);
+ const struct jump_label_patch jlp = __jump_label_patch(entry, type, init);

/*
* As long as only a single processor is running and the code is still
@@ -76,12 +104,11 @@ static inline void __jump_label_transfor
* always nop being the 'currently valid' instruction
*/
if (init || system_state == SYSTEM_BOOTING) {
- text_poke_early((void *)jump_entry_code(entry), opcode,
- JUMP_LABEL_NOP_SIZE);
+ text_poke_early((void *)jump_entry_code(entry), jlp.code, jlp.size);
return;
}

- text_poke_bp((void *)jump_entry_code(entry), opcode, JUMP_LABEL_NOP_SIZE, NULL);
+ text_poke_bp((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL);
}

static void __ref jump_label_transform(struct jump_entry *entry,
@@ -102,7 +129,7 @@ void arch_jump_label_transform(struct ju
bool arch_jump_label_transform_queue(struct jump_entry *entry,
enum jump_label_type type)
{
- const void *opcode;
+ struct jump_label_patch jlp;

if (system_state == SYSTEM_BOOTING) {
/*
@@ -113,9 +140,8 @@ bool arch_jump_label_transform_queue(str
}

mutex_lock(&text_mutex);
- opcode = __jump_label_set_jump_code(entry, type, 0);
- text_poke_queue((void *)jump_entry_code(entry),
- opcode, JUMP_LABEL_NOP_SIZE, NULL);
+ jlp = __jump_label_patch(entry, type, 0);
+ text_poke_queue((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL);
mutex_unlock(&text_mutex);
return true;
}
@@ -137,21 +163,10 @@ __init_or_module void arch_jump_label_tr
enum jump_label_type type)
{
/*
- * This function is called at boot up and when modules are
- * first loaded. Check if the default nop, the one that is
- * inserted at compile time, is the ideal nop. If it is, then
- * we do not need to update the nop, and we can leave it as is.
- * If it is not, then we need to update the nop to the ideal nop.
+ * Rewrite the NOP on init / module-load to ensure we got the ideal
+ * nop. Don't bother with trying to figure out what size and what nop
+ * it should be for now, simply do an unconditional rewrite.
*/
- if (jlstate == JL_STATE_START) {
- const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
- const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
-
- if (memcmp(ideal_nop, default_nop, 5) != 0)
- jlstate = JL_STATE_UPDATE;
- else
- jlstate = JL_STATE_NO_UPDATE;
- }
- if (jlstate == JL_STATE_UPDATE)
+ if (jlstate == JL_STATE_UPDATE || jlstate == JL_STATE_START)
jump_label_transform(entry, type, 1);
}
--- a/arch/x86/realmode/Makefile
+++ b/arch/x86/realmode/Makefile
@@ -10,7 +10,6 @@
# Sanitizer runtimes are unavailable and cannot be linked here.
KASAN_SANITIZE := n
KCSAN_SANITIZE := n
-OBJECT_FILES_NON_STANDARD := y

subdir- := rm

--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -171,9 +171,21 @@ static inline bool jump_entry_is_init(co
return (unsigned long)entry->key & 2UL;
}

-static inline void jump_entry_set_init(struct jump_entry *entry)
+static inline void jump_entry_set_init(struct jump_entry *entry, bool set)
{
- entry->key |= 2;
+ if (set)
+ entry->key |= 2;
+ else
+ entry->key &= ~2;
+}
+
+static inline int jump_entry_size(struct jump_entry *entry)
+{
+#ifdef JUMP_LABEL_NOP_SIZE
+ return JUMP_LABEL_NOP_SIZE;
+#else
+ return arch_jump_entry_size(entry);
+#endif
}

#endif
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -309,7 +309,7 @@ EXPORT_SYMBOL_GPL(jump_label_rate_limit)
static int addr_conflict(struct jump_entry *entry, void *start, void *end)
{
if (jump_entry_code(entry) <= (unsigned long)end &&
- jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE > (unsigned long)start)
+ jump_entry_code(entry) + jump_entry_size(entry) > (unsigned long)start)
return 1;

return 0;
@@ -480,8 +480,8 @@ void __init jump_label_init(void)
if (jump_label_type(iter) == JUMP_LABEL_NOP)
arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);

- if (init_section_contains((void *)jump_entry_code(iter), 1))
- jump_entry_set_init(iter);
+ jump_entry_set_init(iter,
+ init_section_contains((void *)jump_entry_code(iter), 1));

iterk = jump_entry_key(iter);
if (iterk == key)
@@ -627,8 +627,8 @@ static int jump_label_add_module(struct
for (iter = iter_start; iter < iter_stop; iter++) {
struct static_key *iterk;

- if (within_module_init(jump_entry_code(iter), mod))
- jump_entry_set_init(iter);
+ jump_entry_set_init(iter,
+ within_module_init(jump_entry_code(iter), mod));

iterk = jump_entry_key(iter);
if (iterk == key)
--- a/tools/objtool/arch/x86/include/arch/special.h
+++ b/tools/objtool/arch/x86/include/arch/special.h
@@ -9,6 +9,7 @@
#define JUMP_ENTRY_SIZE 16
#define JUMP_ORIG_OFFSET 0
#define JUMP_NEW_OFFSET 4
+#define JUMP_KEY_OFFSET 8

#define ALT_ENTRY_SIZE 13
#define ALT_ORIG_OFFSET 0
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1164,6 +1164,22 @@ static int handle_jump_alt(struct objtoo
return -1;
}

+ if (special_alt->key_addend & 2) {
+ struct reloc *reloc;
+
+ reloc = find_reloc_by_dest_range(file->elf, orig_insn->sec,
+ orig_insn->offset, orig_insn->len);
+ if (reloc) {
+ reloc->type = R_NONE;
+ elf_write_reloc(file->elf, reloc);
+ }
+ elf_write_insn(file->elf, orig_insn->sec,
+ orig_insn->offset, orig_insn->len,
+ arch_nop_insn(orig_insn->len));
+ orig_insn->type = INSN_NOP;
+ return 0;
+ }
+
*new_insn = list_next_entry(orig_insn, list);
return 0;
}
@@ -1709,6 +1725,9 @@ static int decode_sections(struct objtoo
/*
* Must be before add_{jump,call}_destination; for they can add
* magic alternatives we can't actually parse.
+ *
+ * Also; must be before add_jump_destinations() because it will
+ * rewrite JMPs into NOPs -- see handle_jump_alt().
*/
ret = add_special_section_alts(file);
if (ret)
--- a/tools/objtool/include/objtool/special.h
+++ b/tools/objtool/include/objtool/special.h
@@ -27,6 +27,7 @@ struct special_alt {
unsigned long new_off;

unsigned int orig_len, new_len; /* group only */
+ u8 key_addend;
};

int special_get_alts(struct elf *elf, struct list_head *alts);
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -23,6 +23,7 @@ struct special_entry {
unsigned char size, orig, new;
unsigned char orig_len, new_len; /* group only */
unsigned char feature; /* ALTERNATIVE macro CPU feature */
+ unsigned char key; /* jump_label key */
};

struct special_entry entries[] = {
@@ -42,6 +43,7 @@ struct special_entry entries[] = {
.size = JUMP_ENTRY_SIZE,
.orig = JUMP_ORIG_OFFSET,
.new = JUMP_NEW_OFFSET,
+ .key = JUMP_KEY_OFFSET,
},
{
.sec = "__ex_table",
@@ -114,6 +116,18 @@ static int get_alt_entry(struct elf *elf
alt->new_off -= 0x7ffffff0;
}

+ if (entry->key) {
+ struct reloc *key_reloc;
+
+ key_reloc = find_reloc_by_dest(elf, sec, offset + entry->key);
+ if (!key_reloc) {
+ WARN_FUNC("can't find key reloc",
+ sec, offset + entry->key);
+ return -1;
+ }
+ alt->key_addend = key_reloc->addend;
+ }
+
return 0;
}

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