Commit e526a302 authored Oct 27, 2017 by Ricardo Neri Committed by Thomas Gleixner Nov 01, 2017

x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 101b



Section 2.2.1.3 of the Intel 64 and IA-32 Architectures Software
Developer's Manual volume 2A states that when ModRM.mod is zero and
ModRM.rm is 101b, a 32-bit displacement follows the ModRM byte. This means
that none of the registers are used in the computation of the effective
address. A return value of -EDOM indicates callers that they should not
use the value of registers when computing the effective address for the
instruction.

In long mode, the effective address is given by the 32-bit displacement
plus the location of the next instruction. In protected mode, only the
displacement is used.

The instruction decoder takes care of obtaining the displacement.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: ricardo.neri@intel.com
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: Qiaowei Ren <qiaowei.ren@intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Chen Yucong <slaoub@gmail.com>
Cc: Adam Buchbinder <adam.buchbinder@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Garnier <thgarnie@google.com>
Link: https://lkml.kernel.org/r/1509135945-13762-18-git-send-email-ricardo.neri-calderon@linux.intel.com

parent 4efea85f

arch/x86/lib/insn-eval.c

+22 −3

Original line number	Diff line number	Diff line
		@@ -427,6 +427,14 @@ static int get_reg_offset(struct insn insn, struct pt_regs regs,
		switch (type) {
		case REG_TYPE_RM:
		regno = X86_MODRM_RM(insn->modrm.value);

		/*
		* ModRM.mod == 0 and ModRM.rm == 5 means a 32-bit displacement
		* follows the ModRM byte.
		*/
		if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5)
		return -EDOM;

		if (X86_REX_B(insn->rex_prefix.value))
		regno += 8;
		break;
		@@ -770,11 +778,22 @@ void __user insn_get_addr_ref(struct insn insn, struct pt_regs *regs)
		eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
		} else {
		addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
		if (addr_offset < 0)
		/*
		* -EDOM means that we must ignore the address_offset.
		* In such a case, in 64-bit mode the effective address
		* relative to the RIP of the following instruction.
		*/
		if (addr_offset == -EDOM) {
		if (user_64bit_mode(regs))
		eff_addr = (long)regs->ip + insn->length;
		else
		eff_addr = 0;
		} else if (addr_offset < 0) {
		goto out;

		} else {
		eff_addr = regs_get_register(regs, addr_offset);
		}
		}

		eff_addr += insn->displacement.value;
		}

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