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Subject[PATCH 2/4] x86: SROP mitigation: implement signal canaries

This patch implements signal canaries for x86-64, x86-32 and x32.

Signed-off-by: Erik Bosman <erik@minemu.org>

---
arch/x86/Kconfig | 1 +
arch/x86/ia32/ia32_signal.c | 27 +++++++++++++++++++++++++++
arch/x86/include/asm/sigframe.h | 12 ++++++++++++
arch/x86/kernel/signal.c | 41 +++++++++++++++++++++++++++++++++++++++++
4 files changed, 81 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 25d2c6f..83eea28 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -128,6 +128,7 @@ config X86
select HAVE_DEBUG_STACKOVERFLOW
select HAVE_IRQ_EXIT_ON_IRQ_STACK if X86_64
select HAVE_CC_STACKPROTECTOR
+ select HAVE_SIGNAL_CANARY
select GENERIC_CPU_AUTOPROBE
select HAVE_ARCH_AUDITSYSCALL

diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c
index 2206757..1a9285a 100644
--- a/arch/x86/ia32/ia32_signal.c
+++ b/arch/x86/ia32/ia32_signal.c
@@ -212,9 +212,18 @@ asmlinkage long sys32_sigreturn(void)
struct sigframe_ia32 __user *frame = (struct sigframe_ia32 __user *)(regs->sp-8);
sigset_t set;
unsigned int ax;
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif

if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
goto badframe;
+
+#ifdef CONFIG_SIGNAL_CANARY
+ if (__get_user(canary, &frame->canary) || (canary != current->signal_canary))
+ goto badframe;
+#endif
+
if (__get_user(set.sig[0], &frame->sc.oldmask)
|| (_COMPAT_NSIG_WORDS > 1
&& __copy_from_user((((char *) &set.sig) + 4),
@@ -239,11 +248,20 @@ asmlinkage long sys32_rt_sigreturn(void)
struct rt_sigframe_ia32 __user *frame;
sigset_t set;
unsigned int ax;
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif

frame = (struct rt_sigframe_ia32 __user *)(regs->sp - 4);

if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
goto badframe;
+
+#ifdef CONFIG_SIGNAL_CANARY
+ if (__get_user(canary, &frame->canary) || (canary != current->signal_canary))
+ goto badframe;
+#endif
+
if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;

@@ -378,6 +396,11 @@ int ia32_setup_frame(int sig, struct ksignal *ksig,
return -EFAULT;
}

+#ifdef CONFIG_SIGNAL_CANARY
+ if (__put_user(current->signal_canary, &frame->canary))
+ return -EFAULT;
+#endif
+
if (ksig->ka.sa.sa_flags & SA_RESTORER) {
restorer = ksig->ka.sa.sa_restorer;
} else {
@@ -459,6 +482,10 @@ int ia32_setup_rt_frame(int sig, struct ksignal *ksig,
put_user_ex(0, &frame->uc.uc_link);
compat_save_altstack_ex(&frame->uc.uc_stack, regs->sp);

+#ifdef CONFIG_SIGNAL_CANARY
+ put_user_ex(current->signal_canary, &frame->canary);
+#endif
+
if (ksig->ka.sa.sa_flags & SA_RESTORER)
restorer = ksig->ka.sa.sa_restorer;
else
diff --git a/arch/x86/include/asm/sigframe.h b/arch/x86/include/asm/sigframe.h
index 7c7c27c..6af4a9a 100644
--- a/arch/x86/include/asm/sigframe.h
+++ b/arch/x86/include/asm/sigframe.h
@@ -39,6 +39,9 @@ struct sigframe_ia32 {
unsigned long extramask[_NSIG_WORDS-1];
#endif /* CONFIG_IA32_EMULATION */
char retcode[8];
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif
/* fp state follows here */
};

@@ -54,6 +57,9 @@ struct rt_sigframe_ia32 {
#endif /* CONFIG_IA32_EMULATION */
struct ucontext_ia32 uc;
char retcode[8];
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif
/* fp state follows here */
};
#endif /* defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION) */
@@ -64,6 +70,9 @@ struct rt_sigframe {
char __user *pretcode;
struct ucontext uc;
struct siginfo info;
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif
/* fp state follows here */
};

@@ -73,6 +82,9 @@ struct rt_sigframe_x32 {
u64 pretcode;
struct ucontext_x32 uc;
compat_siginfo_t info;
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif
/* fp state follows here */
};

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 9e5de68..0cc4556 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -297,6 +297,11 @@ __setup_frame(int sig, struct ksignal *ksig, sigset_t *set,
return -EFAULT;
}

+#ifdef CONFIG_SIGNAL_CANARY
+ if (__put_user(current->signal_canary, &frame->canary))
+ return -EFAULT;
+#endif
+
if (current->mm->context.vdso)
restorer = VDSO32_SYMBOL(current->mm->context.vdso, sigreturn);
else
@@ -360,6 +365,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
put_user_ex(0, &frame->uc.uc_link);
save_altstack_ex(&frame->uc.uc_stack, regs->sp);

+#ifdef CONFIG_SIGNAL_CANARY
+ put_user_ex(current->signal_canary, &frame->canary);
+#endif
/* Set up to return from userspace. */
restorer = VDSO32_SYMBOL(current->mm->context.vdso, rt_sigreturn);
if (ksig->ka.sa.sa_flags & SA_RESTORER)
@@ -425,6 +433,9 @@ static int __setup_rt_frame(int sig, struct ksignal *ksig,
put_user_ex(0, &frame->uc.uc_link);
save_altstack_ex(&frame->uc.uc_stack, regs->sp);

+#ifdef CONFIG_SIGNAL_CANARY
+ put_user_ex(current->signal_canary, &frame->canary);
+#endif
/* Set up to return from userspace. If provided, use a stub
already in userspace. */
/* x86-64 should always use SA_RESTORER. */
@@ -493,6 +504,10 @@ static int x32_setup_rt_frame(struct ksignal *ksig,
compat_save_altstack_ex(&frame->uc.uc_stack, regs->sp);
put_user_ex(0, &frame->uc.uc__pad0);

+#ifdef CONFIG_SIGNAL_CANARY
+ put_user_ex(current->signal_canary, &frame->canary);
+#endif
+
if (ksig->ka.sa.sa_flags & SA_RESTORER) {
restorer = ksig->ka.sa.sa_restorer;
} else {
@@ -539,11 +554,20 @@ asmlinkage unsigned long sys_sigreturn(void)
struct sigframe __user *frame;
unsigned long ax;
sigset_t set;
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif

frame = (struct sigframe __user *)(regs->sp - 8);

if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
goto badframe;
+
+#ifdef CONFIG_SIGNAL_CANARY
+ if (__get_user(canary, &frame->canary) || (canary != current->signal_canary))
+ goto badframe;
+#endif
+
if (__get_user(set.sig[0], &frame->sc.oldmask) || (_NSIG_WORDS > 1
&& __copy_from_user(&set.sig[1], &frame->extramask,
sizeof(frame->extramask))))
@@ -568,10 +592,19 @@ asmlinkage long sys_rt_sigreturn(void)
struct rt_sigframe __user *frame;
unsigned long ax;
sigset_t set;
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif

frame = (struct rt_sigframe __user *)(regs->sp - sizeof(long));
if (!access_ok(VERIFY_READ, frame, sizeof(*frame)))
goto badframe;
+
+#ifdef CONFIG_SIGNAL_CANARY
+ if (__get_user(canary, &frame->canary) || (canary != current->signal_canary))
+ goto badframe;
+#endif
+
if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;

@@ -780,6 +813,9 @@ asmlinkage long sys32_x32_rt_sigreturn(void)
struct rt_sigframe_x32 __user *frame;
sigset_t set;
unsigned long ax;
+#ifdef CONFIG_SIGNAL_CANARY
+ u32 canary;
+#endif

frame = (struct rt_sigframe_x32 __user *)(regs->sp - 8);

@@ -788,6 +824,11 @@ asmlinkage long sys32_x32_rt_sigreturn(void)
if (__copy_from_user(&set, &frame->uc.uc_sigmask, sizeof(set)))
goto badframe;

+#ifdef CONFIG_SIGNAL_CANARY
+ if (__get_user(canary, &frame->canary) || (canary != current->signal_canary))
+ goto badframe;
+#endif
+
set_current_blocked(&set);

if (restore_sigcontext(regs, &frame->uc.uc_mcontext, &ax))
--
1.9.1


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