Re: [PATCH v7 14/26] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 5
On Wed, 2017-06-07 at 15:15 +0200, Borislav Petkov wrote: > On Fri, May 05, 2017 at 11:17:12AM -0700, Ricardo Neri wrote: > > 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 signals callers that they should not use > > the value of registers when computing the effective address for the > > instruction. > > > > In IA-32e 64-bit mode (long mode), the effective address is given by the > > 32-bit displacement plus the value of RIP of the next instruction. > > In IA-32e compatibility mode (protected mode), only the displacement is > > used. > > > > The instruction decoder takes care of obtaining the displacement. > > ... > > > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c > > index 693e5a8..4f600de 100644 > > --- a/arch/x86/lib/insn-eval.c > > +++ b/arch/x86/lib/insn-eval.c > > @@ -379,6 +379,12 @@ 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); > > > < newline here. Will add the new line. > > > + /* > > +* 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; > > @@ -730,9 +736,21 @@ 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) > > ditto. Will add the new line. > > > + /* > > +* -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) { > > + eff_addr = 0; > > + if (user_64bit_mode(regs)) > > + eff_addr = (long)regs->ip + > > + insn->length; > > Let that line stick out and write it balanced: > > if (addr_offset == -EDOM) { > if (user_64bit_mode(regs)) > eff_addr = (long)regs->ip + > insn->length; > else > eff_addr = 0; > > should be easier parseable this way. Will rewrite as you suggest. Thanks and BR, Ricardo -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH v7 14/26] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 5
On Fri, May 05, 2017 at 11:17:12AM -0700, Ricardo Neri wrote: > 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 signals callers that they should not use > the value of registers when computing the effective address for the > instruction. > > In IA-32e 64-bit mode (long mode), the effective address is given by the > 32-bit displacement plus the value of RIP of the next instruction. > In IA-32e compatibility mode (protected mode), only the displacement is > used. > > The instruction decoder takes care of obtaining the displacement. ... > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c > index 693e5a8..4f600de 100644 > --- a/arch/x86/lib/insn-eval.c > +++ b/arch/x86/lib/insn-eval.c > @@ -379,6 +379,12 @@ 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); < newline here. > + /* > + * 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; > @@ -730,9 +736,21 @@ 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) ditto. > + /* > + * -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) { > + eff_addr = 0; > + if (user_64bit_mode(regs)) > + eff_addr = (long)regs->ip + > +insn->length; Let that line stick out and write it balanced: if (addr_offset == -EDOM) { if (user_64bit_mode(regs)) eff_addr = (long)regs->ip + insn->length; else eff_addr = 0; should be easier parseable this way. -- Regards/Gruss, Boris. SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg) -- -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH v7 14/26] x86/insn-eval: Indicate a 32-bit displacement if ModRM.mod is 0 and ModRM.rm is 5
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 signals callers that they should not use the value of registers when computing the effective address for the instruction. In IA-32e 64-bit mode (long mode), the effective address is given by the 32-bit displacement plus the value of RIP of the next instruction. In IA-32e compatibility mode (protected mode), only the displacement is used. The instruction decoder takes care of obtaining the displacement. Cc: Dave Hansen Cc: Adam Buchbinder Cc: Colin Ian King Cc: Lorenzo Stoakes Cc: Qiaowei Ren Cc: Arnaldo Carvalho de Melo Cc: Masami Hiramatsu Cc: Adrian Hunter Cc: Kees Cook Cc: Thomas Garnier Cc: Peter Zijlstra Cc: Borislav Petkov Cc: Dmitry Vyukov Cc: Ravi V. Shankar Cc: x...@kernel.org Signed-off-by: Ricardo Neri --- arch/x86/lib/insn-eval.c | 22 -- 1 file changed, 20 insertions(+), 2 deletions(-) diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 693e5a8..4f600de 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -379,6 +379,12 @@ 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; @@ -730,9 +736,21 @@ 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) { + eff_addr = 0; + if (user_64bit_mode(regs)) + eff_addr = (long)regs->ip + + insn->length; + } else if (addr_offset < 0) { goto out_err; - eff_addr = regs_get_register(regs, addr_offset); + } else { + eff_addr = regs_get_register(regs, addr_offset); + } } eff_addr += insn->displacement.value; } -- 2.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html