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Subject[PATCH v2 2/4] [RFC] x86/trampfd: Provide support for the trampoline file descriptor
Date
From: "Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>

- Define architecture specific register names
- Architecture specific functions for:
- system call init
- code descriptor check
- data descriptor check
- Fill a page with a trampoline table for:
- 32-bit user process
- 64-bit user process

Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
---
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/x86/include/uapi/asm/ptrace.h | 38 ++++
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/trampfd.c | 238 +++++++++++++++++++++++++
5 files changed, 279 insertions(+)
create mode 100644 arch/x86/kernel/trampfd.c

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index d8f8a1a69ed1..d4f17806c9ab 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -443,3 +443,4 @@
437 i386 openat2 sys_openat2
438 i386 pidfd_getfd sys_pidfd_getfd
439 i386 faccessat2 sys_faccessat2
+440 i386 trampfd sys_trampfd
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 78847b32e137..91b37bc4b6f0 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -360,6 +360,7 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common faccessat2 sys_faccessat2
+440 common trampfd sys_trampfd

#
# x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/arch/x86/include/uapi/asm/ptrace.h b/arch/x86/include/uapi/asm/ptrace.h
index 85165c0edafc..b4be362929b3 100644
--- a/arch/x86/include/uapi/asm/ptrace.h
+++ b/arch/x86/include/uapi/asm/ptrace.h
@@ -9,6 +9,44 @@

#ifndef __ASSEMBLY__

+/*
+ * These register names are to be used by 32-bit applications.
+ */
+enum reg_32_name {
+ x32_min = 0,
+ x32_eax = x32_min,
+ x32_ebx,
+ x32_ecx,
+ x32_edx,
+ x32_esi,
+ x32_edi,
+ x32_ebp,
+ x32_max,
+};
+
+/*
+ * These register names are to be used by 64-bit applications.
+ */
+enum reg_64_name {
+ x64_min = x32_max,
+ x64_rax = x64_min,
+ x64_rbx,
+ x64_rcx,
+ x64_rdx,
+ x64_rsi,
+ x64_rdi,
+ x64_rbp,
+ x64_r8,
+ x64_r9,
+ x64_r10,
+ x64_r11,
+ x64_r12,
+ x64_r13,
+ x64_r14,
+ x64_r15,
+ x64_max,
+};
+
#ifdef __i386__
/* this struct defines the way the registers are stored on the
stack during a system call. */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index e77261db2391..feb7f4f311fd 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -157,3 +157,4 @@ ifeq ($(CONFIG_X86_64),y)
endif

obj-$(CONFIG_IMA_SECURE_AND_OR_TRUSTED_BOOT) += ima_arch.o
+obj-$(CONFIG_TRAMPFD) += trampfd.o
diff --git a/arch/x86/kernel/trampfd.c b/arch/x86/kernel/trampfd.c
new file mode 100644
index 000000000000..7b812c200d01
--- /dev/null
+++ b/arch/x86/kernel/trampfd.c
@@ -0,0 +1,238 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Trampoline FD - X86 support.
+ *
+ * Author: Madhavan T. Venkataraman (madvenka@linux.microsoft.com)
+ *
+ * Copyright (c) 2020, Microsoft Corporation.
+ */
+
+#include <linux/thread_info.h>
+#include <linux/trampfd.h>
+
+#define TRAMPFD_CODE_32_SIZE 24
+#define TRAMPFD_CODE_64_SIZE 40
+
+static inline bool is_compat(void)
+{
+ return (IS_ENABLED(CONFIG_X86_32) ||
+ (IS_ENABLED(CONFIG_COMPAT) && test_thread_flag(TIF_ADDR32)));
+}
+
+/*
+ * trampfd syscall.
+ */
+void trampfd_arch(struct trampfd_info *info)
+{
+ if (is_compat())
+ info->code_size = TRAMPFD_CODE_32_SIZE;
+ else
+ info->code_size = TRAMPFD_CODE_64_SIZE;
+ info->ntrampolines = PAGE_SIZE / info->code_size;
+ info->code_offset = TRAMPFD_CODE_PGOFF << PAGE_SHIFT;
+ info->reserved = 0;
+}
+
+/*
+ * trampfd code descriptor check.
+ */
+int trampfd_code_arch(struct trampfd_code *code)
+{
+ int ntrampolines;
+ int min, max;
+
+ if (is_compat()) {
+ min = x32_min;
+ max = x32_max;
+ ntrampolines = PAGE_SIZE / TRAMPFD_CODE_32_SIZE;
+ } else {
+ min = x64_min;
+ max = x64_max;
+ ntrampolines = PAGE_SIZE / TRAMPFD_CODE_64_SIZE;
+ }
+
+ if (code->reg < min || code->reg >= max)
+ return -EINVAL;
+
+ if (!code->ntrampolines || code->ntrampolines > ntrampolines)
+ return -EINVAL;
+ return 0;
+}
+
+/*
+ * trampfd data descriptor check.
+ */
+int trampfd_data_arch(struct trampfd_data *data)
+{
+ int min, max;
+
+ if (is_compat()) {
+ min = x32_min;
+ max = x32_max;
+ } else {
+ min = x64_min;
+ max = x64_max;
+ }
+
+ if (data->reg < min || data->reg >= max)
+ return -EINVAL;
+ return 0;
+}
+
+/*
+ * X32 register encodings.
+ */
+static unsigned char reg_32[] = {
+ 0, /* x32_eax */
+ 3, /* x32_ebx */
+ 1, /* x32_ecx */
+ 2, /* x32_edx */
+ 6, /* x32_esi */
+ 7, /* x32_edi */
+ 5, /* x32_ebp */
+};
+
+static void trampfd_code_fill_32(struct trampfd *trampfd, char *addr)
+{
+ char *eaddr = addr + PAGE_SIZE;
+ int creg = trampfd->code_reg - x32_min;
+ int dreg = trampfd->data_reg - x32_min;
+ u32 *code = trampfd->code;
+ u32 *data = trampfd->data;
+ int i;
+
+ for (i = 0; i < trampfd->ntrampolines; i++, code++, data++) {
+ /* endbr32 */
+ addr[0] = 0xf3;
+ addr[1] = 0x0f;
+ addr[2] = 0x1e;
+ addr[3] = 0xfb;
+
+ /* mov code, %creg */
+ addr[4] = 0xB8 | reg_32[creg]; /* opcode+reg */
+ memcpy(&addr[5], &code, sizeof(u32)); /* imm32 */
+
+ /* mov (%creg), %creg */
+ addr[9] = 0x8B; /* opcode */
+ addr[10] = 0x00 | /* MODRM.mode */
+ reg_32[creg] << 3 | /* MODRM.reg */
+ reg_32[creg]; /* MODRM.r/m */
+
+ /* mov data, %dreg */
+ addr[11] = 0xB8 | reg_32[dreg]; /* opcode+reg */
+ memcpy(&addr[12], &data, sizeof(u32)); /* imm32 */
+
+ /* mov (%dreg), %dreg */
+ addr[16] = 0x8B; /* opcode */
+ addr[17] = 0x00 | /* MODRM.mode */
+ reg_32[dreg] << 3 | /* MODRM.reg */
+ reg_32[dreg]; /* MODRM.r/m */
+
+ /* jmp *%creg */
+ addr[18] = 0xff; /* opcode */
+ addr[19] = 0xe0 | reg_32[creg]; /* MODRM.r/m */
+
+ /* nopl (%eax) */
+ addr[20] = 0x0f;
+ addr[21] = 0x1f;
+ addr[22] = 0x00;
+
+ /* pad to 4-byte boundary */
+ memset(&addr[23], 0, TRAMPFD_CODE_32_SIZE - 23);
+ addr += TRAMPFD_CODE_32_SIZE;
+ }
+ memset(addr, 0, eaddr - addr);
+}
+
+/*
+ * X64 register encodings.
+ */
+static unsigned char reg_64[] = {
+ 0, /* x64_rax */
+ 3, /* x64_rbx */
+ 1, /* x64_rcx */
+ 2, /* x64_rdx */
+ 6, /* x64_rsi */
+ 7, /* x64_rdi */
+ 5, /* x64_rbp */
+ 8, /* x64_r8 */
+ 9, /* x64_r9 */
+ 10, /* x64_r10 */
+ 11, /* x64_r11 */
+ 12, /* x64_r12 */
+ 13, /* x64_r13 */
+ 14, /* x64_r14 */
+ 15, /* x64_r15 */
+};
+
+static void trampfd_code_fill_64(struct trampfd *trampfd, char *addr)
+{
+ char *eaddr = addr + PAGE_SIZE;
+ int creg = trampfd->code_reg - x64_min;
+ int dreg = trampfd->data_reg - x64_min;
+ u64 *code = trampfd->code;
+ u64 *data = trampfd->data;
+ int i;
+
+ for (i = 0; i < trampfd->ntrampolines; i++, code++, data++) {
+ /* endbr64 */
+ addr[0] = 0xf3;
+ addr[1] = 0x0f;
+ addr[2] = 0x1e;
+ addr[3] = 0xfa;
+
+ /* movabs code, %creg */
+ addr[4] = 0x48 | /* REX.W */
+ ((reg_64[creg] & 0x8) >> 3); /* REX.B */
+ addr[5] = 0xB8 | (reg_64[creg] & 0x7); /* opcode+reg */
+ memcpy(&addr[6], &code, sizeof(u64)); /* imm64 */
+
+ /* movq (%creg), %creg */
+ addr[14] = 0x48 | /* REX.W */
+ ((reg_64[creg] & 0x8) >> 1) | /* REX.R */
+ ((reg_64[creg] & 0x8) >> 3); /* REX.B */
+ addr[15] = 0x8B; /* opcode */
+ addr[16] = 0x00 | /* MODRM.mode */
+ ((reg_64[creg] & 0x7)) << 3 | /* MODRM.reg */
+ ((reg_64[creg] & 0x7)); /* MODRM.r/m */
+
+ /* movabs data, %dreg */
+ addr[17] = 0x48 | /* REX.W */
+ ((reg_64[dreg] & 0x8) >> 3); /* REX.B */
+ addr[18] = 0xB8 | (reg_64[dreg] & 0x7); /* opcode+reg */
+ memcpy(&addr[19], &data, sizeof(u64)); /* imm64 */
+
+ /* movq (%dreg), %dreg */
+ addr[27] = 0x48 | /* REX.W */
+ ((reg_64[dreg] & 0x8) >> 1) | /* REX.R */
+ ((reg_64[dreg] & 0x8) >> 3); /* REX.B */
+ addr[28] = 0x8B; /* opcode */
+ addr[29] = 0x00 | /* MODRM.mode */
+ ((reg_64[dreg] & 0x7)) << 3 | /* MODRM.reg */
+ ((reg_64[dreg] & 0x7)); /* MODRM.r/m */
+
+ /* jmpq *%creg */
+ addr[30] = 0x40 | /* REX.W */
+ ((reg_64[creg] & 0x8) >> 3); /* REX.B */
+ addr[31] = 0xff; /* opcode */
+ addr[32] = 0xe0 | (reg_64[creg] & 0x7); /* MODRM.r/m */
+
+ /* nopl (%rax) */
+ addr[33] = 0x0f;
+ addr[34] = 0x1f;
+ addr[35] = 0x00;
+
+ /* pad to 8-byte boundary */
+ memset(&addr[36], 0, TRAMPFD_CODE_64_SIZE - 36);
+ addr += TRAMPFD_CODE_64_SIZE;
+ }
+ memset(addr, 0, eaddr - addr);
+}
+
+void trampfd_code_fill(struct trampfd *trampfd, char *addr)
+{
+ if (is_compat())
+ trampfd_code_fill_32(trampfd, addr);
+ else
+ trampfd_code_fill_64(trampfd, addr);
+}
--
2.17.1
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