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Message-Id: <20240724000206.451425-1-gatlin.newhouse@gmail.com>
Date: Wed, 24 Jul 2024 00:01:55 +0000
From: Gatlin Newhouse <gatlin.newhouse@...il.com>
To: 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>,
Kees Cook <keescook@...omium.org>,
Marco Elver <elver@...gle.com>,
Andrey Konovalov <andreyknvl@...il.com>,
Andrey Ryabinin <ryabinin.a.a@...il.com>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Bill Wendling <morbo@...gle.com>,
Justin Stitt <justinstitt@...gle.com>,
Gatlin Newhouse <gatlin.newhouse@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Baoquan He <bhe@...hat.com>,
"Mike Rapoport (IBM)" <rppt@...nel.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Changbin Du <changbin.du@...wei.com>,
Rick Edgecombe <rick.p.edgecombe@...el.com>,
Pengfei Xu <pengfei.xu@...el.com>,
Jason Gunthorpe <jgg@...pe.ca>,
Xin Li <xin3.li@...el.com>,
Uros Bizjak <ubizjak@...il.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
linux-kernel@...r.kernel.org,
kasan-dev@...glegroups.com,
linux-hardening@...r.kernel.org,
llvm@...ts.linux.dev
Subject: [PATCH v5] x86/traps: Enable UBSAN traps on x86
Currently ARM architectures extract which specific sanitizer
has caused a trap via encoded data in the trap instruction.[1]
Clang on x86 currently encodes the same data in ud1 instructions
but the x86 handle_bug() and is_valid_bugaddr() functions
currently only look at ud2s.
Bring x86 to parity with arm64, similar to commit 25b84002afb9
("arm64: Support Clang UBSAN trap codes for better reporting").
Enable the reporting of UBSAN sanitizer detail on x86 architectures
compiled with clang when CONFIG_UBSAN_TRAP=y.
[1] Details are in llvm/lib/Target/X86/X86MCInstLower.cpp. See:
https://github.com/llvm/llvm-project/commit/c5978f42ec8e9#diff-bb68d7cd885f41cfc35843998b0f9f534adb60b415f647109e597ce448e92d9f
EmitAndCountInstruction() uses the UD1Lm template, which uses a
OpSize32. See:
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/X86/X86InstrSystem.td#L27
Signed-off-by: Gatlin Newhouse <gatlin.newhouse@...il.com>
---
Changes in v5:
- Added references to the LLVM commits in the commit message from
Kees and Marco's feedback
- Renamed incorrect defines, and removed handle_ubsan_failure()'s
duplicated work per Peter's feedback
Changes in v4:
- Implement Peter's suggestions for decode_bug(), and fix
inconsistent capitalization in hex values.
Changes in v3:
- Address Thomas's remarks about: change log structure,
get_ud_type() instead of is_valid_bugaddr(), handle_bug()
changes, and handle_ubsan_failure().
Changes in v2:
- Name the new constants 'LEN_ASOP' and 'INSN_ASOP' instead of
'LEN_REX' and 'INSN_REX'
- Change handle_ubsan_failure() from enum bug_trap_type to void
function
v1: https://lore.kernel.org/linux-hardening/20240529022043.3661757-1-gatlin.newhouse@gmail.com/
v2: https://lore.kernel.org/linux-hardening/20240601031019.3708758-1-gatlin.newhouse@gmail.com/
v3: https://lore.kernel.org/linux-hardening/20240625032509.4155839-1-gatlin.newhouse@gmail.com/
v4: https://lore.kernel.org/linux-hardening/20240710203250.238782-1-gatlin.newhouse@gmail.com/
---
MAINTAINERS | 2 ++
arch/x86/include/asm/bug.h | 12 ++++++++
arch/x86/include/asm/ubsan.h | 18 ++++++++++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/traps.c | 57 ++++++++++++++++++++++++++++++++----
arch/x86/kernel/ubsan.c | 19 ++++++++++++
6 files changed, 104 insertions(+), 5 deletions(-)
create mode 100644 arch/x86/include/asm/ubsan.h
create mode 100644 arch/x86/kernel/ubsan.c
diff --git a/MAINTAINERS b/MAINTAINERS
index 28e20975c26f..b8512887ffb1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -22635,6 +22635,8 @@ L: kasan-dev@...glegroups.com
L: linux-hardening@...r.kernel.org
S: Supported
T: git git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git for-next/hardening
+F: arch/x86/include/asm/ubsan.h
+F: arch/x86/kernel/ubsan.c
F: Documentation/dev-tools/ubsan.rst
F: include/linux/ubsan.h
F: lib/Kconfig.ubsan
diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
index a3ec87d198ac..751e45ea27ca 100644
--- a/arch/x86/include/asm/bug.h
+++ b/arch/x86/include/asm/bug.h
@@ -13,6 +13,18 @@
#define INSN_UD2 0x0b0f
#define LEN_UD2 2
+/*
+ * In clang we have UD1s reporting UBSAN failures on X86, 64 and 32bit.
+ */
+#define INSN_ASOP 0x67
+#define OPCODE_ESCAPE 0x0f
+#define SECOND_BYTE_OPCODE_UD1 0xb9
+#define SECOND_BYTE_OPCODE_UD2 0x0b
+
+#define BUG_NONE 0xffff
+#define BUG_UD1 0xfffe
+#define BUG_UD2 0xfffd
+
#ifdef CONFIG_GENERIC_BUG
#ifdef CONFIG_X86_32
diff --git a/arch/x86/include/asm/ubsan.h b/arch/x86/include/asm/ubsan.h
new file mode 100644
index 000000000000..1d7c2b4129de
--- /dev/null
+++ b/arch/x86/include/asm/ubsan.h
@@ -0,0 +1,18 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_UBSAN_H
+#define _ASM_X86_UBSAN_H
+
+/*
+ * Clang Undefined Behavior Sanitizer trap mode support.
+ */
+#include <linux/bug.h>
+#include <linux/ubsan.h>
+#include <asm/ptrace.h>
+
+#ifdef CONFIG_UBSAN_TRAP
+void handle_ubsan_failure(struct pt_regs *regs, u32 type);
+#else
+static inline void handle_ubsan_failure(struct pt_regs *regs, u32 type) { return; }
+#endif /* CONFIG_UBSAN_TRAP */
+
+#endif /* _ASM_X86_UBSAN_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 74077694da7d..fe1d9db27500 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -145,6 +145,7 @@ obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o
obj-$(CONFIG_AMD_MEM_ENCRYPT) += sev.o
obj-$(CONFIG_CFI_CLANG) += cfi.o
+obj-$(CONFIG_UBSAN_TRAP) += ubsan.o
obj-$(CONFIG_CALL_THUNKS) += callthunks.o
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4fa0b17e5043..6350d00a6555 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -67,6 +67,7 @@
#include <asm/vdso.h>
#include <asm/tdx.h>
#include <asm/cfi.h>
+#include <asm/ubsan.h>
#ifdef CONFIG_X86_64
#include <asm/x86_init.h>
@@ -91,6 +92,45 @@ __always_inline int is_valid_bugaddr(unsigned long addr)
return *(unsigned short *)addr == INSN_UD2;
}
+/*
+ * Check for UD1 or UD2, accounting for Address Size Override Prefixes.
+ * If it's a UD1, get the ModRM byte to pass along to UBSan.
+ */
+__always_inline int decode_bug(unsigned long addr, u32 *imm)
+{
+ u8 v;
+
+ if (addr < TASK_SIZE_MAX)
+ return BUG_NONE;
+
+ v = *(u8 *)(addr++);
+ if (v == INSN_ASOP)
+ v = *(u8 *)(addr++);
+ if (v != OPCODE_ESCAPE)
+ return BUG_NONE;
+
+ v = *(u8 *)(addr++);
+ if (v == SECOND_BYTE_OPCODE_UD2)
+ return BUG_UD2;
+ if (v != SECOND_BYTE_OPCODE_UD1)
+ return BUG_NONE;
+
+ v = *(u8 *)(addr++);
+ if (X86_MODRM_RM(v) == 4)
+ addr++;
+
+ *imm = 0;
+ if (X86_MODRM_MOD(v) == 1)
+ *imm = *(u8 *)addr;
+ else if (X86_MODRM_MOD(v) == 2)
+ *imm = *(u32 *)addr;
+ else
+ WARN_ONCE(1, "Unexpected MODRM_MOD: %u\n", X86_MODRM_MOD(v));
+
+ return BUG_UD1;
+}
+
+
static nokprobe_inline int
do_trap_no_signal(struct task_struct *tsk, int trapnr, const char *str,
struct pt_regs *regs, long error_code)
@@ -216,6 +256,8 @@ static inline void handle_invalid_op(struct pt_regs *regs)
static noinstr bool handle_bug(struct pt_regs *regs)
{
bool handled = false;
+ int ud_type;
+ u32 imm;
/*
* Normally @regs are unpoisoned by irqentry_enter(), but handle_bug()
@@ -223,7 +265,8 @@ static noinstr bool handle_bug(struct pt_regs *regs)
* irqentry_enter().
*/
kmsan_unpoison_entry_regs(regs);
- if (!is_valid_bugaddr(regs->ip))
+ ud_type = decode_bug(regs->ip, &imm);
+ if (ud_type == BUG_NONE)
return handled;
/*
@@ -236,10 +279,14 @@ static noinstr bool handle_bug(struct pt_regs *regs)
*/
if (regs->flags & X86_EFLAGS_IF)
raw_local_irq_enable();
- if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN ||
- handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
- regs->ip += LEN_UD2;
- handled = true;
+ if (ud_type == BUG_UD2) {
+ if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN ||
+ handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) {
+ regs->ip += LEN_UD2;
+ handled = true;
+ }
+ } else {
+ handle_ubsan_failure(regs, imm);
}
if (regs->flags & X86_EFLAGS_IF)
raw_local_irq_disable();
diff --git a/arch/x86/kernel/ubsan.c b/arch/x86/kernel/ubsan.c
new file mode 100644
index 000000000000..63f819928820
--- /dev/null
+++ b/arch/x86/kernel/ubsan.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Clang Undefined Behavior Sanitizer trap mode support.
+ */
+#include <linux/bug.h>
+#include <linux/string.h>
+#include <linux/printk.h>
+#include <linux/ubsan.h>
+#include <asm/ptrace.h>
+#include <asm/ubsan.h>
+
+/*
+ * Checks for the information embedded in the UD1 trap instruction
+ * for the UB Sanitizer in order to pass along debugging output.
+ */
+void handle_ubsan_failure(struct pt_regs *regs, u32 type)
+{
+ pr_crit("%s at %pS\n", report_ubsan_failure(regs, type), (void *)regs->ip);
+}
--
2.25.1
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