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Subject[PATCH v2 3/4] [RFC] arm64/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/arm64/include/asm/unistd.h | 2 +-
arch/arm64/include/asm/unistd32.h | 2 +
arch/arm64/include/uapi/asm/ptrace.h | 59 +++++++
arch/arm64/kernel/Makefile | 2 +
arch/arm64/kernel/trampfd.c | 244 +++++++++++++++++++++++++++
5 files changed, 308 insertions(+), 1 deletion(-)
create mode 100644 arch/arm64/kernel/trampfd.c

diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 3b859596840d..b3b2019f8d16 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -38,7 +38,7 @@
#define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5)
#define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800)

-#define __NR_compat_syscalls 440
+#define __NR_compat_syscalls 441
#endif

#define __ARCH_WANT_SYS_CLONE
diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index 6d95d0c8bf2f..c0493c5322d9 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@ -885,6 +885,8 @@ __SYSCALL(__NR_openat2, sys_openat2)
__SYSCALL(__NR_pidfd_getfd, sys_pidfd_getfd)
#define __NR_faccessat2 439
__SYSCALL(__NR_faccessat2, sys_faccessat2)
+#define __NR_trampfd 440
+__SYSCALL(__NR_trampfd, sys_trampfd)

/*
* Please add new compat syscalls above this comment and update
diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
index 42cbe34d95ce..2778789c1cbe 100644
--- a/arch/arm64/include/uapi/asm/ptrace.h
+++ b/arch/arm64/include/uapi/asm/ptrace.h
@@ -88,6 +88,65 @@ struct user_pt_regs {
__u64 pstate;
};

+/*
+ * These register names are to be used by 32-bit applications.
+ */
+enum reg_32_name {
+ arm_min,
+ arm_r0 = arm_min,
+ arm_r1,
+ arm_r2,
+ arm_r3,
+ arm_r4,
+ arm_r5,
+ arm_r6,
+ arm_r7,
+ arm_r8,
+ arm_r9,
+ arm_r10,
+ arm_r11,
+ arm_r12,
+ arm_max,
+};
+
+/*
+ * These register names are to be used by 64-bit applications.
+ */
+enum reg_64_name {
+ arm64_min = arm_max,
+ arm64_r0 = arm64_min,
+ arm64_r1,
+ arm64_r2,
+ arm64_r3,
+ arm64_r4,
+ arm64_r5,
+ arm64_r6,
+ arm64_r7,
+ arm64_r8,
+ arm64_r9,
+ arm64_r10,
+ arm64_r11,
+ arm64_r12,
+ arm64_r13,
+ arm64_r14,
+ arm64_r15,
+ arm64_r16,
+ arm64_r17,
+ arm64_r18,
+ arm64_r19,
+ arm64_r20,
+ arm64_r21,
+ arm64_r22,
+ arm64_r23,
+ arm64_r24,
+ arm64_r25,
+ arm64_r26,
+ arm64_r27,
+ arm64_r28,
+ arm64_r29,
+ arm64_max,
+};
+
struct user_fpsimd_state {
__uint128_t vregs[32];
__u32 fpsr;
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index a561cbb91d4d..18d373fb1208 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -71,3 +71,5 @@ extra-y += $(head-y) vmlinux.lds
ifeq ($(CONFIG_DEBUG_EFI),y)
AFLAGS_head.o += -DVMLINUX_PATH="\"$(realpath $(objtree)/vmlinux)\""
endif
+
+obj-$(CONFIG_TRAMPFD) += trampfd.o
diff --git a/arch/arm64/kernel/trampfd.c b/arch/arm64/kernel/trampfd.c
new file mode 100644
index 000000000000..3b40ebb12907
--- /dev/null
+++ b/arch/arm64/kernel/trampfd.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Trampoline FD - ARM64 support.
+ *
+ * Author: Madhavan T. Venkataraman (madvenka@linux.microsoft.com)
+ *
+ * Copyright (c) 2020, Microsoft Corporation.
+ */
+
+#include <linux/thread_info.h>
+#include <asm/compat.h>
+#include <linux/trampfd.h>
+
+#define TRAMPFD_CODE_32_SIZE 28
+#define TRAMPFD_CODE_64_SIZE 48
+
+static inline bool is_compat(void)
+{
+ return is_compat_thread(task_thread_info(current));
+}
+
+/*
+ * 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 = arm_min;
+ max = arm_max;
+ ntrampolines = PAGE_SIZE / TRAMPFD_CODE_32_SIZE;
+ } else {
+ min = arm64_min;
+ max = arm64_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 = arm_min;
+ max = arm_max;
+ } else {
+ min = arm64_min;
+ max = arm64_max;
+ }
+
+ if (data->reg < min || data->reg >= max)
+ return -EINVAL;
+ return 0;
+}
+
+#define MOVARM(ins, reg, imm32) \
+{ \
+ u16 *_imm16 = (u16 *) &(imm32); /* little endian */ \
+ int _hw, _opcode; \
+ \
+ for (_hw = 0; _hw < 2; _hw++) { \
+ /* movw or movt */ \
+ _opcode = _hw ? 0xe3400000 : 0xe3000000; \
+ *ins++ = _opcode | (_imm16[_hw] >> 12) << 16 | \
+ (reg) << 12 | (_imm16[_hw] & 0xFFF); \
+ } \
+}
+
+#define LDRARM(ins, reg) \
+{ \
+ *ins++ = 0xe5900000 | (reg) << 16 | (reg) << 12; \
+}
+
+#define BXARM(ins, reg) \
+{ \
+ *ins++ = 0xe12fff10 | (reg); \
+}
+
+static void trampfd_code_fill_32(struct trampfd *trampfd, char *addr)
+{
+ char *eaddr = addr + PAGE_SIZE;
+ int creg = trampfd->code_reg - arm_min;
+ int dreg = trampfd->data_reg - arm_min;
+ u32 *code = trampfd->code;
+ u32 *data = trampfd->data;
+ u32 *instruction = (u32 *) addr;
+ int i;
+
+ for (i = 0; i < trampfd->ntrampolines; i++, code++, data++) {
+ /*
+ * movw creg, code & 0xFFFF
+ * movt creg, code >> 16
+ */
+ MOVARM(instruction, creg, code);
+
+ /*
+ * ldr creg, [creg]
+ */
+ LDRARM(instruction, creg);
+
+ /*
+ * movw dreg, data & 0xFFFF
+ * movt dreg, data >> 16
+ */
+ MOVARM(instruction, dreg, data);
+
+ /*
+ * ldr dreg, [dreg]
+ */
+ LDRARM(instruction, dreg);
+
+ /*
+ * bx creg
+ */
+ BXARM(instruction, creg);
+ }
+ addr = (char *) instruction;
+ memset(addr, 0, eaddr - addr);
+}
+
+#define MOVQ(ins, reg, imm64) \
+{ \
+ u16 *_imm16 = (u16 *) &(imm64); /* little endian */ \
+ int _hw, _opcode; \
+ \
+ for (_hw = 0; _hw < 4; _hw++) { \
+ /* movz or movk */ \
+ _opcode = _hw ? 0xf2800000 : 0xd2800000; \
+ *ins++ = _opcode | _hw << 21 | _imm16[_hw] << 5 | (reg);\
+ } \
+}
+
+#define LDR(ins, reg) \
+{ \
+ *ins++ = 0xf9400000 | (reg) << 5 | (reg); \
+}
+
+#define BR(ins, reg) \
+{ \
+ *ins++ = 0xd61f0000 | (reg) << 5; \
+}
+
+#define PAD(ins) \
+{ \
+ while ((uintptr_t) ins & 7) \
+ *ins++ = 0; \
+}
+
+static void trampfd_code_fill_64(struct trampfd *trampfd, char *addr)
+{
+ char *eaddr = addr + PAGE_SIZE;
+ int creg = trampfd->code_reg - arm64_min;
+ int dreg = trampfd->data_reg - arm64_min;
+ u64 *code = trampfd->code;
+ u64 *data = trampfd->data;
+ u32 *instruction = (u32 *) addr;
+ int i;
+
+ for (i = 0; i < trampfd->ntrampolines; i++, code++, data++) {
+ /*
+ * Pseudo instruction:
+ *
+ * movq creg, code
+ *
+ * Actual instructions:
+ *
+ * movz creg, code & 0xFFFF
+ * movk creg, (code >> 16) & 0xFFFF, lsl 16
+ * movk creg, (code >> 32) & 0xFFFF, lsl 32
+ * movk creg, (code >> 48) & 0xFFFF, lsl 48
+ */
+ MOVQ(instruction, creg, code);
+
+ /*
+ * ldr creg, [creg]
+ */
+ LDR(instruction, creg);
+
+ /*
+ * Pseudo instruction:
+ *
+ * movq dreg, data
+ *
+ * Actual instructions:
+ *
+ * movz dreg, data & 0xFFFF
+ * movk dreg, (data >> 16) & 0xFFFF, lsl 16
+ * movk dreg, (data >> 32) & 0xFFFF, lsl 32
+ * movk dreg, (data >> 48) & 0xFFFF, lsl 48
+ */
+ MOVQ(instruction, dreg, data);
+
+ /*
+ * ldr dreg, [dreg]
+ */
+ LDR(instruction, dreg);
+
+ /*
+ * br creg
+ */
+ BR(instruction, creg);
+
+ /*
+ * Pad to 8-byte boundary
+ */
+ PAD(instruction);
+ }
+ addr = (char *) instruction;
+ 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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