x86/uprobes: Do not use prefixes.nbytes when looping over prefixes.bytes

commit 4e9a5ae8df5b3365183150f6df49e49dece80d8c upstream

Since insn.prefixes.nbytes can be bigger than the size of
insn.prefixes.bytes[] when a prefix is repeated, the proper check must
be

  insn.prefixes.bytes[i] != 0 and i < 4

instead of using insn.prefixes.nbytes.

Introduce a for_each_insn_prefix() macro for this purpose. Debugged by
Kees Cook <keescook@chromium.org>.

 [ bp: Massage commit message, sync with the respective header in tools/
   and drop "we". ]

Fixes: 2b1444983508 ("uprobes, mm, x86: Add the ability to install and remove uprobes breakpoints")
Reported-by: syzbot+9b64b619f10f19d19a7c@syzkaller.appspotmail.com
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/160697103739.3146288.7437620795200799020.stgit@devnote2
[sudip: adjust context, use old insn.h]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h
index c2c01f84df75f1f9b35a3c898686a82973026d88..3e0e18d376d2c41a9f6a643eed45d1c00963025c 100644 (file)
--- a/arch/x86/include/asm/insn.h
+++ b/arch/x86/include/asm/insn.h
@@ -208,6 +208,21 @@ static inline int insn_offset_immediate(struct insn *insn)
        return insn_offset_displacement(insn) + insn->displacement.nbytes;
 }
 
+/**
+ * for_each_insn_prefix() -- Iterate prefixes in the instruction
+ * @insn: Pointer to struct insn.
+ * @idx:  Index storage.
+ * @prefix: Prefix byte.
+ *
+ * Iterate prefix bytes of given @insn. Each prefix byte is stored in @prefix
+ * and the index is stored in @idx (note that this @idx is just for a cursor,
+ * do not change it.)
+ * Since prefixes.nbytes can be bigger than 4 if some prefixes
+ * are repeated, it cannot be used for looping over the prefixes.
+ */
+#define for_each_insn_prefix(insn, idx, prefix)        \
+       for (idx = 0; idx < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[idx]) != 0; idx++)
+
 #define POP_SS_OPCODE 0x1f
 #define MOV_SREG_OPCODE 0x8e
 

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 73391c1bd2a9a007cb621d670fc08d3ca5a4d27d..52bb7413f3524542f01478e5ba237433b9c33fc7 100644 (file)
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -268,10 +268,11 @@ static volatile u32 good_2byte_insns[256 / 32] = {
 
 static bool is_prefix_bad(struct insn *insn)
 {
+       insn_byte_t p;
        int i;
 
-       for (i = 0; i < insn->prefixes.nbytes; i++) {
-               switch (insn->prefixes.bytes[i]) {
+       for_each_insn_prefix(insn, i, p) {
+               switch (p) {
                case 0x26:      /* INAT_PFX_ES   */
                case 0x2E:      /* INAT_PFX_CS   */
                case 0x36:      /* INAT_PFX_DS   */
@@ -711,6 +712,7 @@ static const struct uprobe_xol_ops branch_xol_ops = {
 static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 {
        u8 opc1 = OPCODE1(insn);
+       insn_byte_t p;
        int i;
 
        switch (opc1) {
@@ -741,8 +743,8 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
         * Intel and AMD behavior differ in 64-bit mode: Intel ignores 66 prefix.
         * No one uses these insns, reject any branch insns with such prefix.
         */
-       for (i = 0; i < insn->prefixes.nbytes; i++) {
-               if (insn->prefixes.bytes[i] == 0x66)
+       for_each_insn_prefix(insn, i, p) {
+               if (p == 0x66)
                        return -ENOTSUPP;
        }
 

diff --git a/tools/objtool/arch/x86/include/asm/insn.h b/tools/objtool/arch/x86/include/asm/insn.h
index c2c01f84df75f1f9b35a3c898686a82973026d88..e9f21f836dfb86bb9c21d1be555c2babe5d6883c 100644 (file)
--- a/tools/objtool/arch/x86/include/asm/insn.h
+++ b/tools/objtool/arch/x86/include/asm/insn.h
@@ -208,6 +208,21 @@ static inline int insn_offset_immediate(struct insn *insn)
        return insn_offset_displacement(insn) + insn->displacement.nbytes;
 }
 
+/**
+ * for_each_insn_prefix() -- Iterate prefixes in the instruction
+ * @insn: Pointer to struct insn.
+ * @idx:  Index storage.
+ * @prefix: Prefix byte.
+ *
+ * Iterate prefix bytes of given @insn. Each prefix byte is stored in @prefix
+ * and the index is stored in @idx (note that this @idx is just for a cursor,
+ * do not change it.)
+ * Since prefixes.nbytes can be bigger than 4 if some prefixes
+ * are repeated, it cannot be used for looping over the prefixes.
+ */
+#define for_each_insn_prefix(insn, idx, prefix)        \
+       for (idx = 0; idx < ARRAY_SIZE(insn->prefixes.bytes) && (prefix = insn->prefixes.bytes[idx]) != 0; idx++)
+
 #define POP_SS_OPCODE 0x1f
 #define MOV_SREG_OPCODE 0x8e