Re: [v2 2/7] x86/mpx: Fail when implicit zero-displacement is used along with R/EBP
On 12/27/2016 02:33 PM, Ricardo Neri wrote: >>> diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c >>> index 6a75a75..71681d0 100644 >>> --- a/arch/x86/mm/mpx.c >>> +++ b/arch/x86/mm/mpx.c >>> @@ -120,6 +120,13 @@ static int get_reg_offset(struct insn *insn, struct >>> pt_regs *regs, >>> >>> case REG_TYPE_BASE: >>> regno = X86_SIB_BASE(insn->sib.value); >>> + if (regno == 5 && X86_MODRM_RM(insn->modrm.value) == 0) { >>> + WARN_ONCE(1, "An explicit displacement is required >>> when %sBP used as SIB base.", >>> + (IS_ENABLED(CONFIG_X86_64) && >>> insn->x86_64) ? >>> + "R13 or R" : "E"); >>> + return -EINVAL; >>> + } >>> + >> Now that I've read the cover letter, I see what's going on. This >> should not warn -- user code can easily trigger this deliberately. > OK, I'll remove it. Are you concerned about the warning printing the > calltrace, even only once? Yes. We don't let userspace spam the kernel, even once. If we have a couple thousand "only once" places, then userspace can overwhelm the kernel log. Also, this needs a much better description of what's going on in the code. Could you add a comment explaining what's going on, and why regno==5, etc...? -- 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: [v2 2/7] x86/mpx: Fail when implicit zero-displacement is used along with R/EBP
On Fri, Dec 23, 2016 at 5:37 PM, Ricardo Neriwrote: > Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software > Developer's Manual volume 2A states that when memory addressing with no > explicit displacement (i.e, mod part of ModR/M is 0), a SIB byte is used > and the base of the SIB byte points to (R/EBP) (i.e., base = 5), an > explicit displacement of 0 must be used. > > Make the address decoder to return -EINVAL in such a case. > > Cc: Dave Hansen > Cc: Adam Buchbinder > Cc: Colin Ian King > Cc: Lorenzo Stoakes > Cc: Qiaowei Ren > Cc: Ravi V. Shankar > Cc: x...@kernel.org > Signed-off-by: Ricardo Neri > --- > arch/x86/mm/mpx.c | 7 +++ > 1 file changed, 7 insertions(+) > > diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c > index 6a75a75..71681d0 100644 > --- a/arch/x86/mm/mpx.c > +++ b/arch/x86/mm/mpx.c > @@ -120,6 +120,13 @@ static int get_reg_offset(struct insn *insn, struct > pt_regs *regs, > > case REG_TYPE_BASE: > regno = X86_SIB_BASE(insn->sib.value); > + if (regno == 5 && X86_MODRM_RM(insn->modrm.value) == 0) { > + WARN_ONCE(1, "An explicit displacement is required > when %sBP used as SIB base.", > + (IS_ENABLED(CONFIG_X86_64) && insn->x86_64) > ? > + "R13 or R" : "E"); > + return -EINVAL; > + } > + Now that I've read the cover letter, I see what's going on. This should not warn -- user code can easily trigger this deliberately. -- 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
[v2 2/7] x86/mpx: Fail when implicit zero-displacement is used along with R/EBP
Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when memory addressing with no explicit displacement (i.e, mod part of ModR/M is 0), a SIB byte is used and the base of the SIB byte points to (R/EBP) (i.e., base = 5), an explicit displacement of 0 must be used. Make the address decoder to return -EINVAL in such a case. Cc: Dave HansenCc: Adam Buchbinder Cc: Colin Ian King Cc: Lorenzo Stoakes Cc: Qiaowei Ren Cc: Ravi V. Shankar Cc: x...@kernel.org Signed-off-by: Ricardo Neri --- arch/x86/mm/mpx.c | 7 +++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c index 6a75a75..71681d0 100644 --- a/arch/x86/mm/mpx.c +++ b/arch/x86/mm/mpx.c @@ -120,6 +120,13 @@ static int get_reg_offset(struct insn *insn, struct pt_regs *regs, case REG_TYPE_BASE: regno = X86_SIB_BASE(insn->sib.value); + if (regno == 5 && X86_MODRM_RM(insn->modrm.value) == 0) { + WARN_ONCE(1, "An explicit displacement is required when %sBP used as SIB base.", + (IS_ENABLED(CONFIG_X86_64) && insn->x86_64) ? + "R13 or R" : "E"); + return -EINVAL; + } + if (X86_REX_B(insn->rex_prefix.value)) regno += 8; break; -- 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