[kernel-hardening] [RFC v2 7/9] Trampoline emulation
aconcernedfossdev at airmail.cc
aconcernedfossdev at airmail.cc
Thu Jun 15 16:47:32 UTC 2017
Thanks for doing this porting work. Look forward to using GRSecurity/PAX
features on ARM eventually. ARM's taking over as we know. x86 is almost
done.
On 2017-06-15 16:42, Salvatore Mesoraca wrote:
> Some programs need to generate part of their code at runtime. Luckily
> enough, in some cases they only generate well-known code sequences (the
> "trampolines") that can be easily recognized and emulated by the
> kernel.
> This way WX Protection can still be active, so a potential attacker
> won't
> be able to generate arbitrary sequences of code, but just those that
> are
> explicitly allowed. This is not ideal, but it's still better than
> having WX
> Protection completely disabled.
> In particular S.A.R.A. is able to recognize trampolines used by GCC for
> nested C functions and libffi's trampolines.
> This feature is implemented only on x86_32 and x86_64.
> The assembly sequences used here were originally obtained from PaX
> source
> code.
>
> Signed-off-by: Salvatore Mesoraca <s.mesoraca16 at gmail.com>
> ---
> security/sara/Kconfig | 17 ++++
> security/sara/include/trampolines.h | 171
> ++++++++++++++++++++++++++++++++++++
> security/sara/wxprot.c | 140
> +++++++++++++++++++++++++++++
> 3 files changed, 328 insertions(+)
> create mode 100644 security/sara/include/trampolines.h
>
> diff --git a/security/sara/Kconfig b/security/sara/Kconfig
> index 6c74069..f406805 100644
> --- a/security/sara/Kconfig
> +++ b/security/sara/Kconfig
> @@ -96,6 +96,23 @@ choice
> Documentation/security/SARA.rst.
> endchoice
>
> +config SECURITY_SARA_WXPROT_EMUTRAMP
> + bool "Enable emulation for some types of trampolines"
> + depends on SECURITY_SARA_WXPROT
> + depends on X86
> + default y
> + help
> + Some programs and libraries need to execute special small code
> + snippets from non-executable memory pages.
> + Most notable examples are the GCC and libffi trampolines.
> + This features make it possible to execute those trampolines even
> + if they reside in non-executable memory pages.
> + This features need to be enabled on a per-executable basis
> + via user-space utilities.
> + See Documentation/security/SARA.rst. for further information.
> +
> + If unsure, answer y.
> +
> config SECURITY_SARA_WXPROT_DISABLED
> bool "WX protection will be disabled at boot."
> depends on SECURITY_SARA_WXPROT
> diff --git a/security/sara/include/trampolines.h
> b/security/sara/include/trampolines.h
> new file mode 100644
> index 0000000..eab0a85
> --- /dev/null
> +++ b/security/sara/include/trampolines.h
> @@ -0,0 +1,171 @@
> +/*
> + * S.A.R.A. Linux Security Module
> + *
> + * Copyright (C) 2017 Salvatore Mesoraca <s.mesoraca16 at gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or
> modify
> + * it under the terms of the GNU General Public License version 2, as
> + * published by the Free Software Foundation.
> + *
> + * Assembly sequences used here were copied from
> + * PaX patch by PaX Team <pageexec at freemail.hu>
> + *
> + */
> +
> +#ifndef __SARA_TRAMPOLINES_H
> +#define __SARA_TRAMPOLINES_H
> +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP
> +
> +
> +/* x86_32 */
> +
> +
> +struct libffi_trampoline_x86_32 {
> + unsigned char mov;
> + unsigned int addr1;
> + unsigned char jmp;
> + unsigned int addr2;
> +} __packed;
> +
> +struct gcc_trampoline_x86_32_type1 {
> + unsigned char mov1;
> + unsigned int addr1;
> + unsigned char mov2;
> + unsigned int addr2;
> + unsigned short jmp;
> +} __packed;
> +
> +struct gcc_trampoline_x86_32_type2 {
> + unsigned char mov;
> + unsigned int addr1;
> + unsigned char jmp;
> + unsigned int addr2;
> +} __packed;
> +
> +union trampolines_x86_32 {
> + struct libffi_trampoline_x86_32 lf;
> + struct gcc_trampoline_x86_32_type1 g1;
> + struct gcc_trampoline_x86_32_type2 g2;
> +};
> +
> +#define is_valid_libffi_trampoline_x86_32(UNION) \
> + (UNION.lf.mov == 0xB8 && \
> + UNION.lf.jmp == 0xE9)
> +
> +#define emulate_libffi_trampoline_x86_32(UNION, REGS) do { \
> + (REGS)->ax = UNION.lf.addr1; \
> + (REGS)->ip = (unsigned int) ((REGS)->ip + \
> + UNION.lf.addr2 + \
> + sizeof(UNION.lf)); \
> +} while (0)
> +
> +#define is_valid_gcc_trampoline_x86_32_type1(UNION, REGS) \
> + (UNION.g1.mov1 == 0xB9 && \
> + UNION.g1.mov2 == 0xB8 && \
> + UNION.g1.jmp == 0xE0FF && \
> + REGS->ip > REGS->sp)
> +
> +#define emulate_gcc_trampoline_x86_32_type1(UNION, REGS) do { \
> + (REGS)->cx = UNION.g1.addr1; \
> + (REGS)->ax = UNION.g1.addr2; \
> + (REGS)->ip = UNION.g1.addr2; \
> +} while (0)
> +
> +#define is_valid_gcc_trampoline_x86_32_type2(UNION, REGS) \
> + (UNION.g2.mov == 0xB9 && \
> + UNION.g2.jmp == 0xE9 && \
> + REGS->ip > REGS->sp)
> +
> +#define emulate_gcc_trampoline_x86_32_type2(UNION, REGS) do { \
> + (REGS)->cx = UNION.g2.addr1; \
> + (REGS)->ip = (unsigned int) ((REGS)->ip + \
> + UNION.g2.addr2 + \
> + sizeof(UNION.g2)); \
> +} while (0)
> +
> +
> +
> +#ifdef CONFIG_X86_64
> +
> +struct libffi_trampoline_x86_64 {
> + unsigned short mov1;
> + unsigned long addr1;
> + unsigned short mov2;
> + unsigned long addr2;
> + unsigned char stcclc;
> + unsigned short jmp1;
> + unsigned char jmp2;
> +} __packed;
> +
> +struct gcc_trampoline_x86_64_type1 {
> + unsigned short mov1;
> + unsigned long addr1;
> + unsigned short mov2;
> + unsigned long addr2;
> + unsigned short jmp1;
> + unsigned char jmp2;
> +} __packed;
> +
> +struct gcc_trampoline_x86_64_type2 {
> + unsigned short mov1;
> + unsigned int addr1;
> + unsigned short mov2;
> + unsigned long addr2;
> + unsigned short jmp1;
> + unsigned char jmp2;
> +} __packed;
> +
> +union trampolines_x86_64 {
> + struct libffi_trampoline_x86_64 lf;
> + struct gcc_trampoline_x86_64_type1 g1;
> + struct gcc_trampoline_x86_64_type2 g2;
> +};
> +
> +#define is_valid_libffi_trampoline_x86_64(UNION) \
> + (UNION.lf.mov1 == 0xBB49 && \
> + UNION.lf.mov2 == 0xBA49 && \
> + (UNION.lf.stcclc == 0xF8 || \
> + UNION.lf.stcclc == 0xF9) && \
> + UNION.lf.jmp1 == 0xFF49 && \
> + UNION.lf.jmp2 == 0xE3)
> +
> +#define emulate_libffi_trampoline_x86_64(UNION, REGS) do { \
> + (REGS)->r11 = UNION.lf.addr1; \
> + (REGS)->r10 = UNION.lf.addr2; \
> + (REGS)->ip = UNION.lf.addr1; \
> + if (UNION.lf.stcclc == 0xF8) \
> + (REGS)->flags &= ~X86_EFLAGS_CF; \
> + else \
> + (REGS)->flags |= X86_EFLAGS_CF; \
> +} while (0)
> +
> +#define is_valid_gcc_trampoline_x86_64_type1(UNION, REGS) \
> + (UNION.g1.mov1 == 0xBB49 && \
> + UNION.g1.mov2 == 0xBA49 && \
> + UNION.g1.jmp1 == 0xFF49 && \
> + UNION.g1.jmp2 == 0xE3 && \
> + REGS->ip > REGS->sp)
> +
> +#define emulate_gcc_trampoline_x86_64_type1(UNION, REGS) do { \
> + (REGS)->r11 = UNION.g1.addr1; \
> + (REGS)->r10 = UNION.g1.addr2; \
> + (REGS)->ip = UNION.g1.addr1; \
> +} while (0)
> +
> +#define is_valid_gcc_trampoline_x86_64_type2(UNION, REGS) \
> + (UNION.g2.mov1 == 0xBB41 && \
> + UNION.g2.mov2 == 0xBA49 && \
> + UNION.g2.jmp1 == 0xFF49 && \
> + UNION.g2.jmp2 == 0xE3 && \
> + REGS->ip > REGS->sp)
> +
> +#define emulate_gcc_trampoline_x86_64_type2(UNION, REGS) do { \
> + (REGS)->r11 = UNION.g2.addr1; \
> + (REGS)->r10 = UNION.g2.addr2; \
> + (REGS)->ip = UNION.g2.addr1; \
> +} while (0)
> +
> +#endif /* CONFIG_X86_64 */
> +
> +#endif /* CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP */
> +#endif /* __SARA_TRAMPOLINES_H */
> diff --git a/security/sara/wxprot.c b/security/sara/wxprot.c
> index f9233a5..38c86be 100644
> --- a/security/sara/wxprot.c
> +++ b/security/sara/wxprot.c
> @@ -22,6 +22,11 @@
> #include <linux/ratelimit.h>
> #include <linux/spinlock.h>
>
> +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP
> +#include <linux/uaccess.h>
> +#include "include/trampolines.h"
> +#endif
> +
> #include "include/sara.h"
> #include "include/sara_data.h"
> #include "include/utils.h"
> @@ -37,6 +42,7 @@
> #define SARA_WXP_COMPLAIN 0x0010
> #define SARA_WXP_VERBOSE 0x0020
> #define SARA_WXP_MMAP 0x0040
> +#define SARA_WXP_EMUTRAMP 0x0100
> #define SARA_WXP_TRANSFER 0x0200
> #define SARA_WXP_NONE 0x0000
> #define SARA_WXP_MPROTECT (SARA_WXP_HEAP | \
> @@ -47,7 +53,12 @@
> SARA_WXP_WXORX | \
> SARA_WXP_COMPLAIN | \
> SARA_WXP_VERBOSE)
> +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP
> +#define SARA_WXP_ALL (__SARA_WXP_ALL | \
> + SARA_WXP_EMUTRAMP)
> +#else /* CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP */
> #define SARA_WXP_ALL __SARA_WXP_ALL
> +#endif /* CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP */
>
> struct wxprot_rule {
> char *path;
> @@ -72,7 +83,11 @@ struct wxprot_config_container {
> static u16 default_flags __ro_after_init =
> CONFIG_SECURITY_SARA_WXPROT_DEFAULT_FLAGS;
>
> +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP
> +static const bool wxprot_emutramp = true;
> +#else
> static const bool wxprot_emutramp;
> +#endif
>
> static void pr_wxp(char *msg)
> {
> @@ -97,6 +112,9 @@ static bool are_flags_valid(u16 flags)
> SARA_WXP_WXORX |
> SARA_WXP_MMAP))))
> return false;
> + if (unlikely(flags & SARA_WXP_EMUTRAMP &&
> + ((flags & SARA_WXP_MPROTECT) != SARA_WXP_MPROTECT)))
> + return false;
> return true;
> }
>
> @@ -366,10 +384,132 @@ static int sara_file_mprotect(struct
> vm_area_struct *vma,
> return 0;
> }
>
> +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP
> +#define PF_PROT (1 << 0)
> +#define PF_USER (1 << 2)
> +#define PF_INSTR (1 << 4)
> +static int sara_pagefault_handler_x86_32(struct pt_regs *regs);
> +static int sara_pagefault_handler_x86_64(struct pt_regs *regs);
> +static int sara_pagefault_handler_x86(struct pt_regs *regs,
> + unsigned long error_code,
> + unsigned long address)
> +{
> + int ret = 0;
> +
> + if (!sara_enabled || !wxprot_enabled ||
> + !(error_code & PF_USER) ||
> + !(error_code & PF_INSTR) ||
> + !(error_code & PF_PROT) ||
> + !(get_current_sara_wxp_flags() & SARA_WXP_EMUTRAMP))
> + return 0;
> +
> + local_irq_enable();
> + might_sleep();
> + might_fault();
> +
> +#ifdef CONFIG_X86_32
> + ret = sara_pagefault_handler_x86_32(regs);
> +#else
> + if (regs->cs == __USER32_CS ||
> + regs->cs & (1<<2)) {
> + if (!(address >> 32)) /* K8 erratum #100 */
> + ret = sara_pagefault_handler_x86_32(regs);
> + } else
> + ret = sara_pagefault_handler_x86_64(regs);
> +#endif
> +
> + return ret;
> +}
> +
> +static int sara_pagefault_handler_x86_32(struct pt_regs *regs)
> +{
> + int ret;
> + void __user *ip = (void __user *) regs->ip;
> + union trampolines_x86_32 t;
> +
> + BUILD_BUG_ON(sizeof(t.lf) > sizeof(t.g1));
> + BUILD_BUG_ON(sizeof(t.g2) > sizeof(t.lf));
> +
> + ret = copy_from_user(&t, ip, sizeof(t.g1));
> + if (ret)
> + ret = copy_from_user(&t, ip, sizeof(t.lf));
> + if (ret)
> + ret = copy_from_user(&t, ip, sizeof(t.g2));
> + if (ret)
> + return 0;
> +
> + if (is_valid_gcc_trampoline_x86_32_type1(t, regs)) {
> + pr_debug("Trampoline: gcc1 x86_32.\n");
> + emulate_gcc_trampoline_x86_32_type1(t, regs);
> + return 1;
> + } else if (is_valid_libffi_trampoline_x86_32(t)) {
> + pr_debug("Trampoline: libffi x86_32.\n");
> + emulate_libffi_trampoline_x86_32(t, regs);
> + return 1;
> + } else if (is_valid_gcc_trampoline_x86_32_type2(t, regs)) {
> + pr_debug("Trampoline: gcc2 x86_32.\n");
> + emulate_gcc_trampoline_x86_32_type2(t, regs);
> + return 1;
> + }
> +
> + pr_debug("Not a trampoline (x86_32).\n");
> +
> + return 0;
> +}
> +
> +#ifdef CONFIG_X86_64
> +static int sara_pagefault_handler_x86_64(struct pt_regs *regs)
> +{
> + int ret;
> + void __user *ip = (void __user *) regs->ip;
> + union trampolines_x86_64 t;
> +
> + BUILD_BUG_ON(sizeof(t.g1) > sizeof(t.lf));
> + BUILD_BUG_ON(sizeof(t.g2) > sizeof(t.g1));
> +
> + ret = copy_from_user(&t, ip, sizeof(t.lf));
> + if (ret)
> + ret = copy_from_user(&t, ip, sizeof(t.g1));
> + if (ret)
> + ret = copy_from_user(&t, ip, sizeof(t.g2));
> + if (ret)
> + return 0;
> +
> + if (is_valid_libffi_trampoline_x86_64(t)) {
> + pr_debug("Trampoline: libffi x86_64.\n");
> + emulate_libffi_trampoline_x86_64(t, regs);
> + return 1;
> + } else if (is_valid_gcc_trampoline_x86_64_type1(t, regs)) {
> + pr_debug("Trampoline: gcc1 x86_64.\n");
> + emulate_gcc_trampoline_x86_64_type1(t, regs);
> + return 1;
> + } else if (is_valid_gcc_trampoline_x86_64_type2(t, regs)) {
> + pr_debug("Trampoline: gcc2 x86_64.\n");
> + emulate_gcc_trampoline_x86_64_type2(t, regs);
> + return 1;
> + }
> +
> + pr_debug("Not a trampoline (x86_64).\n");
> +
> + return 0;
> +
> +}
> +#else /* CONFIG_X86_64 */
> +static inline int sara_pagefault_handler_x86_64(struct pt_regs *regs)
> +{
> + return 0;
> +}
> +#endif /* CONFIG_X86_64 */
> +
> +#endif /* CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP */
> +
> static struct security_hook_list wxprot_hooks[] __ro_after_init = {
> LSM_HOOK_INIT(bprm_set_creds, sara_bprm_set_creds),
> LSM_HOOK_INIT(check_vmflags, sara_check_vmflags),
> LSM_HOOK_INIT(file_mprotect, sara_file_mprotect),
> +#ifdef CONFIG_SECURITY_SARA_WXPROT_EMUTRAMP
> + LSM_HOOK_INIT(pagefault_handler_x86, sara_pagefault_handler_x86),
> +#endif
> };
>
> struct binary_config_header {
--
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