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Date:   Sat, 5 Dec 2020 09:12:56 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     "tip-bot2 for Masami Hiramatsu" <tip-bot2@...utronix.de>,
        linux-tip-commits@...r.kernel.org,
        syzbot+9b64b619f10f19d19a7c@...kaller.appspotmail.com,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Borislav Petkov <bp@...e.de>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        stable@...r.kernel.org, x86@...nel.org
Subject: Re: [tip: x86/urgent] x86/uprobes: Do not use prefixes.nbytes when
 looping over prefixes.bytes

On Fri, 04 Dec 2020 15:04:03 -0000
"tip-bot2 for Masami Hiramatsu" <tip-bot2@...utronix.de> wrote:

> The following commit has been merged into the x86/urgent branch of tip:
> 
> Commit-ID:     9dc23f960adb9ce410ef835b32a2398fdb09c828
> Gitweb:        https://git.kernel.org/tip/9dc23f960adb9ce410ef835b32a2398fdb09c828
> Author:        Masami Hiramatsu <mhiramat@...nel.org>
> AuthorDate:    Thu, 03 Dec 2020 13:50:37 +09:00
> Committer:     Borislav Petkov <bp@...e.de>
> CommitterDate: Fri, 04 Dec 2020 14:32:57 +01:00
> 
> x86/uprobes: Do not use prefixes.nbytes when looping over prefixes.bytes
> 
> 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@...omium.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@...kaller.appspotmail.com
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> Signed-off-by: Borislav Petkov <bp@...e.de>
> Reviewed-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Cc: stable@...r.kernel.org
> Link: https://lkml.kernel.org/r/160697103739.3146288.7437620795200799020.stgit@devnote2
> ---
>  arch/x86/include/asm/insn.h       | 15 +++++++++++++++
>  arch/x86/kernel/uprobes.c         | 10 ++++++----
>  tools/arch/x86/include/asm/insn.h | 17 ++++++++++++++++-
>  3 files changed, 37 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h
> index 5c1ae3e..a8c3d28 100644
> --- a/arch/x86/include/asm/insn.h
> +++ b/arch/x86/include/asm/insn.h
> @@ -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
>  
> diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
> index 3fdaa04..138bdb1 100644
> --- a/arch/x86/kernel/uprobes.c
> +++ b/arch/x86/kernel/uprobes.c
> @@ -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;
>  	}
>  
> diff --git a/tools/arch/x86/include/asm/insn.h b/tools/arch/x86/include/asm/insn.h
> index 568854b..a8c3d28 100644
> --- a/tools/arch/x86/include/asm/insn.h
> +++ b/tools/arch/x86/include/asm/insn.h
> @@ -8,7 +8,7 @@
>   */
>  
>  /* insn_attr_t is defined in inat.h */
> -#include "inat.h"
> +#include <asm/inat.h>

This may break tools/objtool build. Please keep "inat.h".

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>

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