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authorRicardo Neri <ricardo.neri-calderon@linux.intel.com>2017-10-27 23:25:34 +0300
committerThomas Gleixner <tglx@linutronix.de>2017-11-01 23:50:09 +0300
commitff9d78025c519046cfbc212b34f09116685402fc (patch)
treedc9d690dd2227a27f6fae1745ce11de31e8811ff /arch/x86/mm
parentb8d2eff3b1c6e46238a5fb3f56843e9974b4889f (diff)
downloadlinux-ff9d78025c519046cfbc212b34f09116685402fc.tar.xz
x86/mpx: Do not use SIB.index if its value is 100b and ModRM.mod is not 11b
Section 2.2.1.2 of the Intel 64 and IA-32 Architectures Software Developer's Manual volume 2A states that when ModRM.mod !=11b and ModRM.rm = 100b indexed register-indirect addressing is used. In other words, a SIB byte follows the ModRM byte. In the specific case of SIB.index = 100b, the scale*index portion of the computation of the effective address is null. To signal callers of this particular situation, get_reg_offset() can return -EDOM (-EINVAL continues to indicate that an error when decoding the SIB byte). An example of this situation can be the following instruction: 8b 4c 23 80 mov -0x80(%rbx,%riz,1),%rcx ModRM: 0x4c [mod:1b][reg:1b][rm:100b] SIB: 0x23 [scale:0b][index:100b][base:11b] Displacement: 0x80 (1-byte, as per ModRM.mod = 1b) The %riz 'register' indicates a null index. In long mode, a REX prefix may be used. When a REX prefix is present, REX.X adds a fourth bit to the register selection of SIB.index. This gives the ability to refer to all the 16 general purpose registers. When REX.X is 1b and SIB.index is 100b, the index is indicated in %r12. In our example, this would look like: 42 8b 4c 23 80 mov -0x80(%rbx,%r12,1),%rcx REX: 0x42 [W:0b][R:0b][X:1b][B:0b] ModRM: 0x4c [mod:1b][reg:1b][rm:100b] SIB: 0x23 [scale:0b][.X: 1b, index:100b][.B:0b, base:11b] Displacement: 0x80 (1-byte, as per ModRM.mod = 1b) %r12 is a valid register to use in the scale*index part of the effective address computation. 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: Adan Hawthorn <adanhawthorn@gmail.com> 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: 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: Jonathan Corbet <corbet@lwn.net> Cc: Jiri Slaby <jslaby@suse.cz> Cc: Nathan Howard <liverlint@gmail.com> Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com> Cc: Chris Metcalf <cmetcalf@mellanox.com> Cc: Brian Gerst <brgerst@gmail.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: Joe Perches <joe@perches.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Link: https://lkml.kernel.org/r/1509135945-13762-8-git-send-email-ricardo.neri-calderon@linux.intel.com
Diffstat (limited to 'arch/x86/mm')
-rw-r--r--arch/x86/mm/mpx.c21
1 files changed, 19 insertions, 2 deletions
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 57e5bf58ea34..2ad1d4a42fcc 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -110,6 +110,15 @@ 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 ModRM.mod != 3 and SIB.index = 4 the scale*index
+ * portion of the address computation is null. This is
+ * true only if REX.X is 0. In such a case, the SIB index
+ * is used in the address computation.
+ */
+ if (X86_MODRM_MOD(insn->modrm.value) != 3 && regno == 4)
+ return -EDOM;
break;
case REG_TYPE_BASE:
@@ -160,11 +169,19 @@ static void __user *mpx_get_addr_ref(struct insn *insn, struct pt_regs *regs)
goto out;
indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
- if (indx_offset < 0)
+ /*
+ * A negative offset generally means a error, except
+ * -EDOM, which means that the contents of the register
+ * should not be used as index.
+ */
+ if (indx_offset == -EDOM)
+ indx = 0;
+ else if (indx_offset < 0)
goto out;
+ else
+ indx = regs_get_register(regs, indx_offset);
base = regs_get_register(regs, base_offset);
- indx = regs_get_register(regs, indx_offset);
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {