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Date: Fri, 23 Dec 2016 17:37:39 -0800 From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com> To: Ingo Molnar <mingo@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...e.de>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org, x86@...nel.org, <linux-msdos@...r.kernel.org>, <wine-devel@...ehq.org>, Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Adam Buchbinder <adam.buchbinder@...il.com>, Colin Ian King <colin.king@...onical.com>, Lorenzo Stoakes <lstoakes@...il.com>, Qiaowei Ren <qiaowei.ren@...el.com>, "Ravi V . Shankar" <ravi.v.shankar@...el.com> Subject: [v2 1/7] x86/mpx: Do not use SIB index if index points to R/ESP Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when memory addressing is used (i.e., mod part of ModR/M is not 3), a SIB byte is used and the index of the SIB byte points to the R/ESP (i.e.,index = 4), the index should not be used in the computation of the memory address. An example of such instruction could be insn -0x80(%rsp) This is represented as: [opcode] 4c 24 80 ModR/M: mod: 1, reg: 1: r/m: 4 (R/ESP) SIB 24: sc: 0, index: 100 (R/ESP), base(R/ESP): 100 Displacement -0x80 The correct address is (base) + displacement; no index is used. Care is taken to allow R12 to be used as index, which is a valid scenario. Cc: Dave Hansen <dave.hansen@...ux.intel.com> Cc: Adam Buchbinder <adam.buchbinder@...il.com> Cc: Colin Ian King <colin.king@...onical.com> Cc: Lorenzo Stoakes <lstoakes@...il.com> Cc: Qiaowei Ren <qiaowei.ren@...el.com> Cc: Ravi V. Shankar <ravi.v.shankar@...el.com> Cc: x86@...nel.org Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com> --- arch/x86/mm/mpx.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 324e571..6a75a75 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -109,6 +109,13 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, regno = X86_SIB_INDEX(insn->sib.value); if (X86_REX_X(insn->rex_prefix.value)) regno += 8; + /* + * If mod !=3, SP is not used as index. Check is done after + * looking at REX.X This is because R12 can be used as an + * index. + */ + if (regno == 4 && X86_MODRM_RM(insn->modrm.value) != 3) + return 0; break; case REG_TYPE_BASE: @@ -161,7 +168,10 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs) goto out_err; base = regs_get_register(regs, base_offset); - indx = regs_get_register(regs, indx_offset); + if (indx_offset) + indx = regs_get_register(regs, indx_offset); + else + indx = 0; addr = base + indx * (1 << X86_SIB_SCALE(sib)); } else { addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM); -- 2.9.3
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