From: Peter Zijlstra <peterz@infradead.org>
Date: Tue, 14 Jun 2022 23:16:03 +0200
Subject: objtool: Add entry UNRET validation
Git-commit: a09a6e2399ba0595c3042b3164f3ca68a3cff33e
Patch-mainline: v5.19-rc7
References: bsc#1199657 CVE-2022-29900 CVE-2022-29901
Since entry asm is tricky, add a validation pass that ensures the
retbleed mitigation has been done before the first actual RET
instruction.
Entry points are those that either have UNWIND_HINT_ENTRY, which acts
as UNWIND_HINT_EMPTY but marks the instruction as an entry point, or
those that have UWIND_HINT_IRET_REGS at +0.
This is basically a variant of validate_branch() that is
intra-function and it will simply follow all branches from marked
entry points and ensures that all paths lead to ANNOTATE_UNRET_END.
If a path hits RET or an indirection the path is a fail and will be
reported.
There are 3 ANNOTATE_UNRET_END instances:
- UNTRAIN_RET itself
- exception from-kernel; this path doesn't need UNTRAIN_RET
- all early exceptions; these also don't need UNTRAIN_RET
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
---
arch/x86/entry/entry_64.S | 3
arch/x86/entry/entry_64_compat.S | 6 -
arch/x86/include/asm/nospec-branch.h | 12 ++
arch/x86/include/asm/unwind_hints.h | 4
arch/x86/kernel/head_64.S | 3
include/linux/objtool.h | 3
tools/include/linux/objtool.h | 3
tools/objtool/builtin-check.c | 3
tools/objtool/check.c | 177 +++++++++++++++++++++++++++++++-
tools/objtool/include/objtool/arch.h | 1
tools/objtool/include/objtool/builtin.h | 2
tools/objtool/include/objtool/check.h | 7 +
12 files changed, 214 insertions(+), 10 deletions(-)
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -49,7 +49,7 @@
* 0(%ebp) arg6
*/
SYM_CODE_START(entry_SYSENTER_compat)
- UNWIND_HINT_EMPTY
+ UNWIND_HINT_ENTRY
/* Interrupts are off on entry. */
SWAPGS
@@ -202,7 +202,7 @@ SYM_CODE_END(entry_SYSENTER_compat)
* 0(%esp) arg6
*/
SYM_CODE_START(entry_SYSCALL_compat)
- UNWIND_HINT_EMPTY
+ UNWIND_HINT_ENTRY
/* Interrupts are off on entry. */
swapgs
@@ -346,7 +346,7 @@ SYM_CODE_END(entry_SYSCALL_compat)
* ebp arg6
*/
SYM_CODE_START(entry_INT80_compat)
- UNWIND_HINT_EMPTY
+ UNWIND_HINT_ENTRY
/*
* Interrupts are off on entry.
*/
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -85,7 +85,7 @@
*/
SYM_CODE_START(entry_SYSCALL_64)
- UNWIND_HINT_EMPTY
+ UNWIND_HINT_ENTRY
swapgs
/* tss.sp2 is scratch space. */
@@ -1052,6 +1052,7 @@ SYM_CODE_START_LOCAL(error_entry)
*/
.Lerror_entry_done_lfence:
FENCE_SWAPGS_KERNEL_ENTRY
+ ANNOTATE_UNRET_END
RET
.Lbstep_iret:
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -82,6 +82,17 @@
#define ANNOTATE_UNRET_SAFE ANNOTATE_RETPOLINE_SAFE
/*
+ * Abuse ANNOTATE_RETPOLINE_SAFE on a NOP to indicate UNRET_END, should
+ * eventually turn into it's own annotation.
+ */
+.macro ANNOTATE_UNRET_END
+#ifdef CONFIG_DEBUG_ENTRY
+ ANNOTATE_RETPOLINE_SAFE
+ nop
+#endif
+.endm
+
+/*
* JMP_NOSPEC and CALL_NOSPEC macros can be used instead of a simple
* indirect jmp/call which may be susceptible to the Spectre variant 2
* attack.
@@ -131,6 +142,7 @@
*/
.macro UNTRAIN_RET
#ifdef CONFIG_RETPOLINE
+ ANNOTATE_UNRET_END
ALTERNATIVE_2 "", \
"call zen_untrain_ret", X86_FEATURE_UNRET, \
"call entry_ibpb", X86_FEATURE_ENTRY_IBPB
--- a/arch/x86/include/asm/unwind_hints.h
+++ b/arch/x86/include/asm/unwind_hints.h
@@ -11,6 +11,10 @@
UNWIND_HINT sp_reg=ORC_REG_UNDEFINED type=UNWIND_HINT_TYPE_CALL end=1
.endm
+.macro UNWIND_HINT_ENTRY
+ UNWIND_HINT sp_reg=ORC_REG_UNDEFINED type=UNWIND_HINT_TYPE_ENTRY end=1
+.endm
+
.macro UNWIND_HINT_REGS base=%rsp offset=0 indirect=0 extra=1 partial=0
.if \base == %rsp
.if \indirect
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -312,6 +312,8 @@ SYM_CODE_END(start_cpu0)
SYM_CODE_START_NOALIGN(vc_boot_ghcb)
UNWIND_HINT_IRET_REGS offset=8
+ ANNOTATE_UNRET_END
+
/* Build pt_regs */
PUSH_AND_CLEAR_REGS
@@ -369,6 +371,7 @@ SYM_CODE_START(early_idt_handler_array)
SYM_CODE_END(early_idt_handler_array)
SYM_CODE_START_LOCAL(early_idt_handler_common)
+ ANNOTATE_UNRET_END
/*
* The stack is the hardware frame, an error code or zero, and the
* vector number.
--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -32,11 +32,14 @@ struct unwind_hint {
*
* UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
* Useful for code which doesn't have an ELF function annotation.
+ *
+ * UNWIND_HINT_ENTRY: machine entry without stack, SYSCALL/SYSENTER etc.
*/
#define UNWIND_HINT_TYPE_CALL 0
#define UNWIND_HINT_TYPE_REGS 1
#define UNWIND_HINT_TYPE_REGS_PARTIAL 2
#define UNWIND_HINT_TYPE_FUNC 3
+#define UNWIND_HINT_TYPE_ENTRY 4
#ifdef CONFIG_STACK_VALIDATION
--- a/tools/include/linux/objtool.h
+++ b/tools/include/linux/objtool.h
@@ -32,11 +32,14 @@ struct unwind_hint {
*
* UNWIND_HINT_FUNC: Generate the unwind metadata of a callable function.
* Useful for code which doesn't have an ELF function annotation.
+ *
+ * UNWIND_HINT_ENTRY: machine entry without stack, SYSCALL/SYSENTER etc.
*/
#define UNWIND_HINT_TYPE_CALL 0
#define UNWIND_HINT_TYPE_REGS 1
#define UNWIND_HINT_TYPE_REGS_PARTIAL 2
#define UNWIND_HINT_TYPE_FUNC 3
+#define UNWIND_HINT_TYPE_ENTRY 4
#ifdef CONFIG_STACK_VALIDATION
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -20,7 +20,7 @@
#include <objtool/objtool.h>
bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
- validate_dup, vmlinux, mcount, noinstr, backup, sls;
+ validate_dup, vmlinux, mcount, noinstr, backup, sls, ibt, unret;
static const char * const check_usage[] = {
"objtool check [<options>] file.o",
@@ -45,6 +45,7 @@ const struct option check_options[] = {
OPT_BOOLEAN('l', "vmlinux", &vmlinux, "vmlinux.o validation"),
OPT_BOOLEAN('M', "mcount", &mcount, "generate __mcount_loc"),
OPT_BOOLEAN('B', "backup", &backup, "create .orig files before modification"),
+ OPT_BOOLEAN(0, "unret", &unret, "validate entry unret placement"),
OPT_BOOLEAN('S', "sls", &sls, "validate straight-line-speculation"),
OPT_END(),
};
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1833,6 +1833,24 @@ static int read_unwind_hints(struct objt
insn->hint = true;
+ if (hint->type == UNWIND_HINT_TYPE_REGS_PARTIAL) {
+ struct symbol *sym = find_symbol_by_offset(insn->sec, insn->offset);
+
+ if (sym && sym->bind == STB_GLOBAL) {
+ if (ibt && insn->type != INSN_ENDBR && !insn->noendbr) {
+ WARN_FUNC("UNWIND_HINT_IRET_REGS without ENDBR",
+ insn->sec, insn->offset);
+ }
+
+ insn->entry = 1;
+ }
+ }
+
+ if (hint->type == UNWIND_HINT_TYPE_ENTRY) {
+ hint->type = UNWIND_HINT_TYPE_CALL;
+ insn->entry = 1;
+ }
+
if (hint->type == UNWIND_HINT_TYPE_FUNC) {
insn->cfi = &func_cfi;
continue;
@@ -1881,8 +1899,9 @@ static int read_retpoline_hints(struct o
if (insn->type != INSN_JUMP_DYNAMIC &&
insn->type != INSN_CALL_DYNAMIC &&
- insn->type != INSN_RETURN) {
- WARN_FUNC("retpoline_safe hint not an indirect jump/call/ret",
+ insn->type != INSN_RETURN &&
+ insn->type != INSN_NOP) {
+ WARN_FUNC("retpoline_safe hint not an indirect jump/call/ret/nop",
insn->sec, insn->offset);
return -1;
}
@@ -2982,8 +3001,8 @@ static int validate_branch(struct objtoo
return 1;
}
- visited = 1 << state.uaccess;
- if (insn->visited) {
+ visited = VISITED_BRANCH << state.uaccess;
+ if (insn->visited & VISITED_BRANCH_MASK) {
if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
return 1;
@@ -3211,6 +3230,145 @@ static int validate_unwind_hints(struct
return warnings;
}
+/*
+ * Validate rethunk entry constraint: must untrain RET before the first RET.
+ *
+ * Follow every branch (intra-function) and ensure ANNOTATE_UNRET_END comes
+ * before an actual RET instruction.
+ */
+static int validate_entry(struct objtool_file *file, struct instruction *insn)
+{
+ struct instruction *next, *dest;
+ int ret, warnings = 0;
+
+ for (;;) {
+ next = next_insn_to_validate(file, insn);
+
+ if (insn->visited & VISITED_ENTRY)
+ return 0;
+
+ insn->visited |= VISITED_ENTRY;
+
+ if (!insn->ignore_alts && !list_empty(&insn->alts)) {
+ struct alternative *alt;
+ bool skip_orig = false;
+
+ list_for_each_entry(alt, &insn->alts, list) {
+ if (alt->skip_orig)
+ skip_orig = true;
+
+ ret = validate_entry(file, alt->insn);
+ if (ret) {
+ if (backtrace)
+ BT_FUNC("(alt)", insn);
+ return ret;
+ }
+ }
+
+ if (skip_orig)
+ return 0;
+ }
+
+ switch (insn->type) {
+
+ case INSN_CALL_DYNAMIC:
+ case INSN_JUMP_DYNAMIC:
+ case INSN_JUMP_DYNAMIC_CONDITIONAL:
+ WARN_FUNC("early indirect call", insn->sec, insn->offset);
+ return 1;
+
+ case INSN_JUMP_UNCONDITIONAL:
+ case INSN_JUMP_CONDITIONAL:
+ if (!is_sibling_call(insn)) {
+ if (!insn->jump_dest) {
+ WARN_FUNC("unresolved jump target after linking?!?",
+ insn->sec, insn->offset);
+ return -1;
+ }
+ ret = validate_entry(file, insn->jump_dest);
+ if (ret) {
+ if (backtrace) {
+ BT_FUNC("(branch%s)", insn,
+ insn->type == INSN_JUMP_CONDITIONAL ? "-cond" : "");
+ }
+ return ret;
+ }
+
+ if (insn->type == INSN_JUMP_UNCONDITIONAL)
+ return 0;
+
+ break;
+ }
+
+ /* fallthrough */
+ case INSN_CALL:
+ dest = find_insn(file, insn->call_dest->sec,
+ insn->call_dest->offset);
+ if (!dest) {
+ WARN("Unresolved function after linking!?: %s",
+ insn->call_dest->name);
+ return -1;
+ }
+
+ ret = validate_entry(file, dest);
+ if (ret) {
+ if (backtrace)
+ BT_FUNC("(call)", insn);
+ return ret;
+ }
+ /*
+ * If a call returns without error, it must have seen UNTRAIN_RET.
+ * Therefore any non-error return is a success.
+ */
+ return 0;
+
+ case INSN_RETURN:
+ WARN_FUNC("RET before UNTRAIN", insn->sec, insn->offset);
+ return 1;
+
+ case INSN_NOP:
+ if (insn->retpoline_safe)
+ return 0;
+ break;
+
+ default:
+ break;
+ }
+
+ if (!next) {
+ WARN_FUNC("teh end!", insn->sec, insn->offset);
+ return -1;
+ }
+ insn = next;
+ }
+
+ return warnings;
+}
+
+/*
+ * Validate that all branches starting at 'insn->entry' encounter UNRET_END
+ * before RET.
+ */
+static int validate_unret(struct objtool_file *file)
+{
+ struct instruction *insn;
+ int ret, warnings = 0;
+
+ for_each_insn(file, insn) {
+ if (!insn->entry)
+ continue;
+
+ ret = validate_entry(file, insn);
+ if (ret < 0) {
+ WARN_FUNC("Failed UNRET validation", insn->sec, insn->offset);
+ return ret;
+ }
+ warnings += ret;
+ }
+
+ return warnings;
+}
+
static int validate_retpoline(struct objtool_file *file)
{
struct instruction *insn;
@@ -3488,6 +3646,17 @@ int check(struct objtool_file *file)
warnings += ret;
}
+ if (unret) {
+ /*
+ * Must be after validate_branch() and friends, it plays
+ * further games with insn->visited.
+ */
+ ret = validate_unret(file);
+ if (ret < 0)
+ return ret;
+ warnings += ret;
+ }
+
ret = create_static_call_sections(file);
if (ret < 0)
goto out;
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -27,6 +27,7 @@ enum insn_type {
INSN_STD,
INSN_CLD,
INSN_TRAP,
+ INSN_ENDBR,
INSN_OTHER,
};
--- a/tools/objtool/include/objtool/builtin.h
+++ b/tools/objtool/include/objtool/builtin.h
@@ -9,7 +9,7 @@
extern const struct option check_options[];
extern bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats,
- validate_dup, vmlinux, mcount, noinstr, backup, sls;
+ validate_dup, vmlinux, mcount, noinstr, backup, sls, ibt, unret;
extern int cmd_parse_options(int argc, const char **argv, const char * const usage[]);
--- a/tools/objtool/include/objtool/check.h
+++ b/tools/objtool/include/objtool/check.h
@@ -48,6 +48,8 @@ struct instruction {
bool dead_end, ignore, ignore_alts;
bool hint;
bool retpoline_safe;
+ bool noendbr;
+ bool entry;
s8 instr;
u8 visited;
struct alt_group *alt_group;
@@ -62,6 +64,11 @@ struct instruction {
struct cfi_state *cfi;
};
+#define VISITED_BRANCH 0x01
+#define VISITED_BRANCH_UACCESS 0x02
+#define VISITED_BRANCH_MASK 0x03
+#define VISITED_ENTRY 0x04
+
static inline bool is_static_jump(struct instruction *insn)
{
return insn->type == INSN_JUMP_CONDITIONAL ||