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Mon, 28 Dec 2020 10:51:21 -0800 (PST) Date: Mon, 28 Dec 2020 10:51:15 -0800 From: Sean Christopherson To: Borislav Petkov Cc: Andy Lutomirski , Masami Hiramatsu , X86 ML , LKML Subject: Re: [PATCH v1 04/19] x86/insn-eval: Handle return values from the decoder Message-ID: References: <20201223174233.28638-1-bp@alien8.de> <20201223174233.28638-5-bp@alien8.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201223174233.28638-5-bp@alien8.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 23, 2020, Borislav Petkov wrote: > From: Borislav Petkov > > Now that the different instruction-inspecting functions return a value, > test that and return early from callers if error has been encountered. > > While at it, do not call insn_get_modrm() when calling > insn_get_displacement() because latter will make sure to call > insn_get_modrm() if ModRM hasn't been parsed yet. > > Signed-off-by: Borislav Petkov > --- > arch/x86/lib/insn-eval.c | 19 +++++++++++++------ > 1 file changed, 13 insertions(+), 6 deletions(-) > > diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c > index 265d23a0c334..7e49aaf5454c 100644 > --- a/arch/x86/lib/insn-eval.c > +++ b/arch/x86/lib/insn-eval.c > @@ -1106,18 +1106,21 @@ static int get_eff_addr_modrm_16(struct insn *insn, struct pt_regs *regs, > * @base_offset will have a register, as an offset from the base of pt_regs, > * that can be used to resolve the associated segment. > * > - * -EINVAL on error. > + * Negative value on error. > */ > static int get_eff_addr_sib(struct insn *insn, struct pt_regs *regs, > int *base_offset, long *eff_addr) > { > long base, indx; > int indx_offset; > + int ret; > > if (insn->addr_bytes != 8 && insn->addr_bytes != 4) > return -EINVAL; > > - insn_get_modrm(insn); > + ret = insn_get_modrm(insn); This patch is incomplete/inconsistent, and arguably wrong. - get_eff_addr_reg() and get_eff_addr_modrm() still ignore the return of insn_get_modrm() after this patch. - Calling insn_get_modrm() from get_eff_addr_sib() is unnecessary (unless the caller passed uninitialized garbage in @insn) as get_eff_addr_sib() is called if and only if sib.nbytes!=0, and sib.nbytes can be non-zero if and only if the modrm and sib have been got. - get_addr_ref_16() does insn_get_displacement, i.e. guarantees the modrm is parsed, while the 32/64 variants do not. What about adding a prereq patch (or three) to call insn_get_displacement() in insn_get_addr_ref() prior to switching on insn->addr_bytes? Then the various internal helpers could be changed to either omit the sanity checks entirely or WARN on invalid calls? Or better yet, add an INSN_WARN_ON() macro that compiles out the checks by default? E.g. something like: diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 7e49aaf5454c..348969146e0f 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -928,12 +928,8 @@ static int get_seg_base_limit(struct insn *insn, struct pt_regs *regs, diff --git a/arch/x86/lib/insn-eval.c b/arch/x86/lib/insn-eval.c index 7e49aaf5454c..348969146e0f 100644 --- a/arch/x86/lib/insn-eval.c +++ b/arch/x86/lib/insn-eval.c @@ -928,12 +928,8 @@ static int get_seg_base_limit(struct insn *insn, struct pt_regs *regs, static int get_eff_addr_reg(struct insn *insn, struct pt_regs *regs, int *regoff, long *eff_addr) { - insn_get_modrm(insn); - - if (!insn->modrm.nbytes) - return -EINVAL; - - if (X86_MODRM_MOD(insn->modrm.value) != 3) + if (INSN_WARN_ON(!insn->modrm.got || !insn->modrm.nbytes || + X86_MODRM_MOD(insn->modrm.value) != 3) return -EINVAL; *regoff = get_reg_offset(insn, regs, REG_TYPE_RM); @@ -978,15 +974,9 @@ static int get_eff_addr_modrm(struct insn *insn, struct pt_regs *regs, { long tmp; - if (insn->addr_bytes != 8 && insn->addr_bytes != 4) - return -EINVAL; - - insn_get_modrm(insn); - - if (!insn->modrm.nbytes) - return -EINVAL; - - if (X86_MODRM_MOD(insn->modrm.value) > 2) + if (INSN_WARN_ON((insn->addr_bytes != 8 && insn->addr_bytes != 4) || + !insn->modrm.got || !insn->modrm.nbytes || + X86_MODRM_MOD(insn->modrm.value) > 2) return -EINVAL; *regoff = get_reg_offset(insn, regs, REG_TYPE_RM); @@ -1046,15 +1036,8 @@ static int get_eff_addr_modrm_16(struct insn *insn, struct pt_regs *regs, int addr_offset1, addr_offset2, ret; short addr1 = 0, addr2 = 0, displacement; - if (insn->addr_bytes != 2) - return -EINVAL; - - insn_get_modrm(insn); - - if (!insn->modrm.nbytes) - return -EINVAL; - - if (X86_MODRM_MOD(insn->modrm.value) > 2) + if (WARN_ON_ONCE(insn->addr_bytes != 2 || !insn->modrm.got || + !insn->modrm.nbytes || insn->modrm.value > 2)) return -EINVAL; ret = get_reg_offset_16(insn, regs, &addr_offset1, &addr_offset2); @@ -1199,10 +1182,7 @@ static void __user *get_addr_ref_16(struct insn *insn, struct pt_regs *regs) short eff_addr; long tmp; - if (insn_get_displacement(insn)) - goto out; - - if (insn->addr_bytes != 2) + if (INSN_WARN_ON(insn->addr_bytes != 2)) goto out; if (X86_MODRM_MOD(insn->modrm.value) == 3) { @@ -1263,7 +1243,7 @@ static void __user *get_addr_ref_32(struct insn *insn, struct pt_regs *regs) long tmp; int ret; - if (insn->addr_bytes != 4) + if (INSN_WARN_ON(insn->addr_bytes != 4)) goto out; if (X86_MODRM_MOD(insn->modrm.value) == 3) { @@ -1356,7 +1336,7 @@ static void __user *get_addr_ref_64(struct insn *insn, struct pt_regs *regs) int regoff, ret; long eff_addr; - if (insn->addr_bytes != 8) + if (INSN_WARN_ON(insn->addr_bytes != 8)) goto out; if (X86_MODRM_MOD(insn->modrm.value) == 3) { @@ -1408,6 +1388,9 @@ void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs) if (!insn || !regs) return (void __user *)-1L; + if (insn_get_displacement(insn)) + return (void __user *)-1L; + switch (insn->addr_bytes) { case 2: return get_addr_ref_16(insn, regs);