Re: [v3 PATCH 03/10] x86/mpx, x86/insn: Relocate insn util functions to a new insn-kernel

[Masami Hiramatsu <mhiramat@kernel.org>]

On Wed, 25 Jan 2017 12:23:46 -0800
Ricardo Neri <ricardo.neri-calderon@linux.intel.com> wrote:

> Other kernel submodules can benefit from using the utility functions
> defined in mpx.c to obtain the addresses and values of operands contained
> in the general purpose registers. An instance of this is the emulation code
> used for instructions protected by the Intel User-Mode Instruction
> Prevention feature.
> 
> Thus, these functions are relocated to a new insn-kernel.c file. The reason
> to not relocate these utilities into insn.c is that the latter solely
> analyses instructions given by a struct insn without any knowledge of the
> kernel context. This new utilities insn-kernel.c aims to be used within the
> context of the kernel. For instance, it can be used to determine memory
> addresses as encoded in the contents of the general purpose registers.

What would you mean the "kernel context" here? Extracting the register offset
or an address by decoding instruction seems not depending on where the
context (pt_regs) in kernel or user...

Of course, this is a kind of "evaluation" of instruction, so it might be
better to split it to other file, but I think insn-eval.c is better.

Thank you,

> 
> These utilities come with a separate header. This is to avoid taking insn.c
> out of sync from the instructions decoders under tools/obj and tools/perf.
> This also avoids adding cumbersome #ifdef's for the #include'd files
> required to decode instructions in a kernel context.
> 
> Functions are simply relocated. There are not functional or indentation
> changes.
> 
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
> Cc: Colin Ian King <colin.king@canonical.com>
> Cc: Lorenzo Stoakes <lstoakes@gmail.com>
> Cc: Qiaowei Ren <qiaowei.ren@intel.com>
> Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Cc: Adrian Hunter <adrian.hunter@intel.com>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Thomas Garnier <thgarnie@google.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Ravi V. Shankar <ravi.v.shankar@intel.com>
> Cc: x86@kernel.org
> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> ---
>  arch/x86/include/asm/insn-kernel.h |  16 ++++
>  arch/x86/lib/Makefile              |   2 +-
>  arch/x86/lib/insn-kernel.c         | 147 +++++++++++++++++++++++++++++++++++++
>  arch/x86/mm/mpx.c                  | 140 +----------------------------------
>  4 files changed, 166 insertions(+), 139 deletions(-)
>  create mode 100644 arch/x86/include/asm/insn-kernel.h
>  create mode 100644 arch/x86/lib/insn-kernel.c
> 
> diff --git a/arch/x86/include/asm/insn-kernel.h b/arch/x86/include/asm/insn-kernel.h
> new file mode 100644
> index 0000000..aef416a
> --- /dev/null
> +++ b/arch/x86/include/asm/insn-kernel.h
> @@ -0,0 +1,16 @@
> +#ifndef _ASM_X86_INSN_KERNEL_H
> +#define _ASM_X86_INSN_KERNEL_H
> +/*
> + * A collection of utility functions for x86 instruction analysis to be
> + * used in a kernel context. Useful when, for instance, making sense
> + * of the registers indicated by operands.
> + */
> +
> +#include <linux/compiler.h>
> +#include <linux/bug.h>
> +#include <linux/err.h>
> +#include <asm/ptrace.h>
> +
> +void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs);
> +
> +#endif /* _ASM_X86_INSN_KERNEL_H */
> diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
> index 34a7413..d33eff1 100644
> --- a/arch/x86/lib/Makefile
> +++ b/arch/x86/lib/Makefile
> @@ -23,7 +23,7 @@ lib-y := delay.o misc.o cmdline.o cpu.o
>  lib-y += usercopy_$(BITS).o usercopy.o getuser.o putuser.o
>  lib-y += memcpy_$(BITS).o
>  lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem.o
> -lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o
> +lib-$(CONFIG_INSTRUCTION_DECODER) += insn.o inat.o insn-kernel.o
>  lib-$(CONFIG_RANDOMIZE_BASE) += kaslr.o
>  
>  obj-y += msr.o msr-reg.o msr-reg-export.o hweight.o
> diff --git a/arch/x86/lib/insn-kernel.c b/arch/x86/lib/insn-kernel.c
> new file mode 100644
> index 0000000..8072abe
> --- /dev/null
> +++ b/arch/x86/lib/insn-kernel.c
> @@ -0,0 +1,147 @@
> +/*
> + * Utility functions for x86 operand and address decoding
> + *
> + * Copyright (C) Intel Corporation 2016
> + */
> +#include <linux/kernel.h>
> +#include <linux/string.h>
> +#include <asm/inat.h>
> +#include <asm/insn.h>
> +#include <asm/insn-kernel.h>
> +
> +enum reg_type {
> +	REG_TYPE_RM = 0,
> +	REG_TYPE_INDEX,
> +	REG_TYPE_BASE,
> +};
> +
> +static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
> +			  enum reg_type type)
> +{
> +	int regno = 0;
> +
> +	static const int regoff[] = {
> +		offsetof(struct pt_regs, ax),
> +		offsetof(struct pt_regs, cx),
> +		offsetof(struct pt_regs, dx),
> +		offsetof(struct pt_regs, bx),
> +		offsetof(struct pt_regs, sp),
> +		offsetof(struct pt_regs, bp),
> +		offsetof(struct pt_regs, si),
> +		offsetof(struct pt_regs, di),
> +#ifdef CONFIG_X86_64
> +		offsetof(struct pt_regs, r8),
> +		offsetof(struct pt_regs, r9),
> +		offsetof(struct pt_regs, r10),
> +		offsetof(struct pt_regs, r11),
> +		offsetof(struct pt_regs, r12),
> +		offsetof(struct pt_regs, r13),
> +		offsetof(struct pt_regs, r14),
> +		offsetof(struct pt_regs, r15),
> +#endif
> +	};
> +	int nr_registers = ARRAY_SIZE(regoff);
> +	/*
> +	 * Don't possibly decode a 32-bit instructions as
> +	 * reading a 64-bit-only register.
> +	 */
> +	if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64)
> +		nr_registers -= 8;
> +
> +	switch (type) {
> +	case REG_TYPE_RM:
> +		regno = X86_MODRM_RM(insn->modrm.value);
> +		if (X86_REX_B(insn->rex_prefix.value))
> +			regno += 8;
> +		break;
> +
> +	case REG_TYPE_INDEX:
> +		regno = X86_SIB_INDEX(insn->sib.value);
> +		if (X86_REX_X(insn->rex_prefix.value))
> +			regno += 8;
> +		/*
> +		 * If mod !=3, register R/ESP (regno=4) is not used as index in
> +		 * the address computation. Check is done after looking at REX.X
> +		 * This is because R12 (regno=12) can be used as an index.
> +		 */
> +		if (regno == 4 && X86_MODRM_MOD(insn->modrm.value) != 3)
> +			return -EINVAL;
> +		break;
> +
> +	case REG_TYPE_BASE:
> +		regno = X86_SIB_BASE(insn->sib.value);
> +		/*
> +		 * If R/EBP (regno = 5) is indicated in the base part of the SIB
> +		 * byte, an explicit displacement must be specified. In other
> +		 * words, the mod part of the ModRM byte cannot be zero.
> +		 */
> +		if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
> +			return -EINVAL;
> +
> +		if (X86_REX_B(insn->rex_prefix.value))
> +			regno += 8;
> +		break;
> +
> +	default:
> +		pr_err("invalid register type");
> +		BUG();
> +		break;
> +	}
> +
> +	if (regno >= nr_registers) {
> +		WARN_ONCE(1, "decoded an instruction with an invalid register");
> +		return -EINVAL;
> +	}
> +	return regoff[regno];
> +}
> +
> +/*
> + * return the address being referenced be instruction
> + * for rm=3 returning the content of the rm reg
> + * for rm!=3 calculates the address using SIB and Disp
> + */
> +void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
> +{
> +	unsigned long addr, base, indx;
> +	int addr_offset, base_offset, indx_offset;
> +	insn_byte_t sib;
> +
> +	insn_get_modrm(insn);
> +	insn_get_sib(insn);
> +	sib = insn->sib.value;
> +
> +	if (X86_MODRM_MOD(insn->modrm.value) == 3) {
> +		addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
> +		if (addr_offset < 0)
> +			goto out_err;
> +		addr = regs_get_register(regs, addr_offset);
> +	} else {
> +		if (insn->sib.nbytes) {
> +			base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
> +			if (base_offset < 0)
> +				goto out_err;
> +
> +			indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
> +			/*
> +			 * A negative offset means that the register cannot be
> +			 * be used as an index.
> +			 */
> +			if (indx_offset < 0)
> +				indx = 0;
> +			else
> +				indx = regs_get_register(regs, indx_offset);
> +
> +			base = regs_get_register(regs, base_offset);
> +			addr = base + indx * (1 << X86_SIB_SCALE(sib));
> +		} else {
> +			addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
> +			if (addr_offset < 0)
> +				goto out_err;
> +			addr = regs_get_register(regs, addr_offset);
> +		}
> +		addr += insn->displacement.value;
> +	}
> +	return (void __user *)addr;
> +out_err:
> +	return (void __user *)-1;
> +}
> diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
> index c59a851..ca6fe13 100644
> --- a/arch/x86/mm/mpx.c
> +++ b/arch/x86/mm/mpx.c
> @@ -11,6 +11,7 @@
>  #include <linux/sched/sysctl.h>
>  
>  #include <asm/insn.h>
> +#include <asm/insn-kernel.h>
>  #include <asm/mman.h>
>  #include <asm/mmu_context.h>
>  #include <asm/mpx.h>
> @@ -59,143 +60,6 @@ static unsigned long mpx_mmap(unsigned long len)
>  	return addr;
>  }
>  
> -enum reg_type {
> -	REG_TYPE_RM = 0,
> -	REG_TYPE_INDEX,
> -	REG_TYPE_BASE,
> -};
> -
> -static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
> -			  enum reg_type type)
> -{
> -	int regno = 0;
> -
> -	static const int regoff[] = {
> -		offsetof(struct pt_regs, ax),
> -		offsetof(struct pt_regs, cx),
> -		offsetof(struct pt_regs, dx),
> -		offsetof(struct pt_regs, bx),
> -		offsetof(struct pt_regs, sp),
> -		offsetof(struct pt_regs, bp),
> -		offsetof(struct pt_regs, si),
> -		offsetof(struct pt_regs, di),
> -#ifdef CONFIG_X86_64
> -		offsetof(struct pt_regs, r8),
> -		offsetof(struct pt_regs, r9),
> -		offsetof(struct pt_regs, r10),
> -		offsetof(struct pt_regs, r11),
> -		offsetof(struct pt_regs, r12),
> -		offsetof(struct pt_regs, r13),
> -		offsetof(struct pt_regs, r14),
> -		offsetof(struct pt_regs, r15),
> -#endif
> -	};
> -	int nr_registers = ARRAY_SIZE(regoff);
> -	/*
> -	 * Don't possibly decode a 32-bit instructions as
> -	 * reading a 64-bit-only register.
> -	 */
> -	if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64)
> -		nr_registers -= 8;
> -
> -	switch (type) {
> -	case REG_TYPE_RM:
> -		regno = X86_MODRM_RM(insn->modrm.value);
> -		if (X86_REX_B(insn->rex_prefix.value))
> -			regno += 8;
> -		break;
> -
> -	case REG_TYPE_INDEX:
> -		regno = X86_SIB_INDEX(insn->sib.value);
> -		if (X86_REX_X(insn->rex_prefix.value))
> -			regno += 8;
> -		/*
> -		 * If mod !=3, register R/ESP (regno=4) is not used as index in
> -		 * the address computation. Check is done after looking at REX.X
> -		 * This is because R12 (regno=12) can be used as an index.
> -		 */
> -		if (regno == 4 && X86_MODRM_MOD(insn->modrm.value) != 3)
> -			return -EINVAL;
> -		break;
> -
> -	case REG_TYPE_BASE:
> -		regno = X86_SIB_BASE(insn->sib.value);
> -		/*
> -		 * If R/EBP (regno = 5) is indicated in the base part of the SIB
> -		 * byte, an explicit displacement must be specified. In other
> -		 * words, the mod part of the ModRM byte cannot be zero.
> -		 */
> -		if (regno == 5 && X86_MODRM_MOD(insn->modrm.value) == 0)
> -			return -EINVAL;
> -
> -		if (X86_REX_B(insn->rex_prefix.value))
> -			regno += 8;
> -		break;
> -
> -	default:
> -		pr_err("invalid register type");
> -		BUG();
> -		break;
> -	}
> -
> -	if (regno >= nr_registers) {
> -		WARN_ONCE(1, "decoded an instruction with an invalid register");
> -		return -EINVAL;
> -	}
> -	return regoff[regno];
> -}
> -
> -/*
> - * return the address being referenced be instruction
> - * for rm=3 returning the content of the rm reg
> - * for rm!=3 calculates the address using SIB and Disp
> - */
> -static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
> -{
> -	unsigned long addr, base, indx;
> -	int addr_offset, base_offset, indx_offset;
> -	insn_byte_t sib;
> -
> -	insn_get_modrm(insn);
> -	insn_get_sib(insn);
> -	sib = insn->sib.value;
> -
> -	if (X86_MODRM_MOD(insn->modrm.value) == 3) {
> -		addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
> -		if (addr_offset < 0)
> -			goto out_err;
> -		addr = regs_get_register(regs, addr_offset);
> -	} else {
> -		if (insn->sib.nbytes) {
> -			base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
> -			if (base_offset < 0)
> -				goto out_err;
> -
> -			indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
> -			/*
> -			 * A negative offset means that the register cannot be
> -			 * be used as an index.
> -			 */
> -			if (indx_offset < 0)
> -				indx = 0;
> -			else
> -				indx = regs_get_register(regs, indx_offset);
> -
> -			base = regs_get_register(regs, base_offset);
> -			addr = base + indx * (1 << X86_SIB_SCALE(sib));
> -		} else {
> -			addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
> -			if (addr_offset < 0)
> -				goto out_err;
> -			addr = regs_get_register(regs, addr_offset);
> -		}
> -		addr += insn->displacement.value;
> -	}
> -	return (void __user *)addr;
> -out_err:
> -	return (void __user *)-1;
> -}
> -
>  static int mpx_insn_decode(struct insn *insn,
>  			   struct pt_regs *regs)
>  {
> @@ -308,7 +172,7 @@ siginfo_t *mpx_generate_siginfo(struct pt_regs *regs)
>  	info->si_signo = SIGSEGV;
>  	info->si_errno = 0;
>  	info->si_code = SEGV_BNDERR;
> -	info->si_addr = mpx_get_addr_ref(&insn, regs);
> +	info->si_addr = insn_get_addr_ref(&insn, regs);
>  	/*
>  	 * We were not able to extract an address from the instruction,
>  	 * probably because there was something invalid in it.
> -- 
> 2.9.3
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>