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

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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: 2b14449835 ("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
This commit is contained in:
Masami Hiramatsu 2020-12-03 13:50:37 +09:00 committed by Borislav Petkov
parent 8dcc0e19df
commit 4e9a5ae8df
3 changed files with 36 additions and 4 deletions
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15
arch/x86/include/asm/insn.h
View File

@ -201,6 +201,21 @@ 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

10
arch/x86/kernel/uprobes.c
View File

@ -255,12 +255,13 @@ 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++) {
for_each_insn_prefix(insn, i, p) {
insn_attr_t attr;
attr = inat_get_opcode_attribute(insn->prefixes.bytes[i]);
attr = inat_get_opcode_attribute(p);
switch (attr) {
case INAT_MAKE_PREFIX(INAT_PFX_ES):
case INAT_MAKE_PREFIX(INAT_PFX_CS):
@ -715,6 +716,7 @@ static const struct uprobe_xol_ops push_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) {
@ -746,8 +748,8 @@ 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;
}

15
tools/arch/x86/include/asm/insn.h
View File

@ -201,6 +201,21 @@ 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