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Message-Id: <20200916150826.5990-5-madvenka@linux.microsoft.com>
Date: Wed, 16 Sep 2020 10:08:26 -0500
From: madvenka@...ux.microsoft.com
To: kernel-hardening@...ts.openwall.com,
linux-api@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
linux-fsdevel@...r.kernel.org,
linux-integrity@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org,
oleg@...hat.com,
x86@...nel.org,
madvenka@...ux.microsoft.com
Subject: [PATCH v2 4/4] [RFC] arm/trampfd: Provide support for the trampoline file descriptor
From: "Madhavan T. Venkataraman" <madvenka@...ux.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,
Signed-off-by: Madhavan T. Venkataraman <madvenka@...ux.microsoft.com>
---
arch/arm/include/uapi/asm/ptrace.h | 21 +++++
arch/arm/kernel/Makefile | 1 +
arch/arm/kernel/trampfd.c | 124 +++++++++++++++++++++++++++++
arch/arm/tools/syscall.tbl | 1 +
4 files changed, 147 insertions(+)
create mode 100644 arch/arm/kernel/trampfd.c
diff --git a/arch/arm/include/uapi/asm/ptrace.h b/arch/arm/include/uapi/asm/ptrace.h
index e61c65b4018d..598047768f9b 100644
--- a/arch/arm/include/uapi/asm/ptrace.h
+++ b/arch/arm/include/uapi/asm/ptrace.h
@@ -151,6 +151,27 @@ struct pt_regs {
#define ARM_r0 uregs[0]
#define ARM_ORIG_r0 uregs[17]
+/*
+ * 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,
+};
+
/*
* The size of the user-visible VFP state as seen by PTRACE_GET/SETVFPREGS
* and core dumps.
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 89e5d864e923..652c54c2f19a 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -105,5 +105,6 @@ obj-$(CONFIG_SMP) += psci_smp.o
endif
obj-$(CONFIG_HAVE_ARM_SMCCC) += smccc-call.o
+obj-$(CONFIG_TRAMPFD) += trampfd.o
extra-y := $(head-y) vmlinux.lds
diff --git a/arch/arm/kernel/trampfd.c b/arch/arm/kernel/trampfd.c
new file mode 100644
index 000000000000..45146ed489e8
--- /dev/null
+++ b/arch/arm/kernel/trampfd.c
@@ -0,0 +1,124 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Trampoline FD - ARM support.
+ *
+ * Author: Madhavan T. Venkataraman (madvenka@...ux.microsoft.com)
+ *
+ * Copyright (c) 2020, Microsoft Corporation.
+ */
+
+#include <linux/thread_info.h>
+#include <linux/trampfd.h>
+
+#define TRAMPFD_CODE_SIZE 28
+
+/*
+ * trampfd syscall.
+ */
+void trampfd_arch(struct trampfd_info *info)
+{
+ info->code_size = TRAMPFD_CODE_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;
+
+ min = arm_min;
+ max = arm_max;
+ ntrampolines = PAGE_SIZE / TRAMPFD_CODE_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;
+
+ min = arm_min;
+ max = arm_max;
+
+ if (data->reg < min || data->reg >= max)
+ return -EINVAL;
+ return 0;
+}
+
+#define MOVW(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 LDR(ins, reg) \
+{ \
+ *ins++ = 0xe5900000 | (reg) << 16 | (reg) << 12; \
+}
+
+#define BX(ins, reg) \
+{ \
+ *ins++ = 0xe12fff10 | (reg); \
+}
+
+void trampfd_code_fill(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
+ */
+ MOVW(instruction, creg, code);
+
+ /*
+ * ldr creg, [creg]
+ */
+ LDR(instruction, creg);
+
+ /*
+ * movw dreg, data & 0xFFFF
+ * movt dreg, data >> 16
+ */
+ MOVW(instruction, dreg, data);
+
+ /*
+ * ldr dreg, [dreg]
+ */
+ LDR(instruction, dreg);
+
+ /*
+ * bx creg
+ */
+ BX(instruction, creg);
+ }
+ addr = (char *) instruction;
+ memset(addr, 0, eaddr - addr);
+}
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index d5cae5ffede0..85dcbc9e08ee 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -452,3 +452,4 @@
437 common openat2 sys_openat2
438 common pidfd_getfd sys_pidfd_getfd
439 common faccessat2 sys_faccessat2
+440 common trampfd sys_trampfd
--
2.17.1
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