[PATCH v2 0/3] fix function type mismatches in syscall wrappers

[PATCH v2 0/3] fix function type mismatches in syscall wrappers

[Sami Tolvanen]

These patches fix type mismatches in arm64 syscall wrapper
definitions, which trip indirect call checks with Control-Flow
Integrity.

Changes in v2:
- more informative commit message for the syscall_fn_t change
- added a patch for fixing sys_ni_syscall

Sami Tolvanen (3):
  arm64: fix syscall_fn_t type
  arm64: use the correct function type in SYSCALL_DEFINE0
  arm64: use the correct function type for __arm64_sys_ni_syscall

 arch/arm64/include/asm/syscall.h         |  2 +-
 arch/arm64/include/asm/syscall_wrapper.h | 18 +++++++++---------
 arch/arm64/kernel/sys.c                  | 14 +++++++++-----
 arch/arm64/kernel/sys32.c                | 12 ++++++++----
 4 files changed, 27 insertions(+), 19 deletions(-)

-- 
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[PATCH v2 1/3] arm64: fix syscall_fn_t type

[Sami Tolvanen]

Syscall wrappers in <asm/syscall_wrapper.h> use const struct pt_regs *
as the argument type. Use const in syscall_fn_t as well to fix indirect
call type mismatches with Control-Flow Integrity checking.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
---
 arch/arm64/include/asm/syscall.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index a179df3674a1a..6206ab9bfcfc5 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -20,7 +20,7 @@
 #include <linux/compat.h>
 #include <linux/err.h>
 
-typedef long (*syscall_fn_t)(struct pt_regs *regs);
+typedef long (*syscall_fn_t)(const struct pt_regs *regs);
 
 extern const syscall_fn_t sys_call_table[];
 
-- 
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[PATCH v2 2/3] arm64: use the correct function type in SYSCALL_DEFINE0

[Sami Tolvanen]

Although a syscall defined using SYSCALL_DEFINE0 doesn't accept
parameters, use the correct function type to avoid indirect call
type mismatches with Control-Flow Integrity checking.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/arm64/include/asm/syscall_wrapper.h | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/syscall_wrapper.h b/arch/arm64/include/asm/syscall_wrapper.h
index a4477e515b798..507d0ee6bc690 100644
--- a/arch/arm64/include/asm/syscall_wrapper.h
+++ b/arch/arm64/include/asm/syscall_wrapper.h
@@ -30,10 +30,10 @@
 	}										\
 	static inline long __do_compat_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
 
-#define COMPAT_SYSCALL_DEFINE0(sname)					\
-	asmlinkage long __arm64_compat_sys_##sname(void);		\
-	ALLOW_ERROR_INJECTION(__arm64_compat_sys_##sname, ERRNO);	\
-	asmlinkage long __arm64_compat_sys_##sname(void)
+#define COMPAT_SYSCALL_DEFINE0(sname)							\
+	asmlinkage long __arm64_compat_sys_##sname(const struct pt_regs *__unused);	\
+	ALLOW_ERROR_INJECTION(__arm64_compat_sys_##sname, ERRNO);			\
+	asmlinkage long __arm64_compat_sys_##sname(const struct pt_regs *__unused)
 
 #define COND_SYSCALL_COMPAT(name) \
 	cond_syscall(__arm64_compat_sys_##name);
@@ -62,11 +62,11 @@
 	static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__))
 
 #ifndef SYSCALL_DEFINE0
-#define SYSCALL_DEFINE0(sname)					\
-	SYSCALL_METADATA(_##sname, 0);				\
-	asmlinkage long __arm64_sys_##sname(void);		\
-	ALLOW_ERROR_INJECTION(__arm64_sys_##sname, ERRNO);	\
-	asmlinkage long __arm64_sys_##sname(void)
+#define SYSCALL_DEFINE0(sname)							\
+	SYSCALL_METADATA(_##sname, 0);						\
+	asmlinkage long __arm64_sys_##sname(const struct pt_regs *__unused);	\
+	ALLOW_ERROR_INJECTION(__arm64_sys_##sname, ERRNO);			\
+	asmlinkage long __arm64_sys_##sname(const struct pt_regs *__unused)
 #endif
 
 #ifndef COND_SYSCALL
-- 
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[PATCH v2 3/3] arm64: use the correct function type for __arm64_sys_ni_syscall

[Sami Tolvanen]

Calling sys_ni_syscall through a syscall_fn_t pointer trips indirect
call Control-Flow Integrity checking due to a function type
mismatch. Use SYSCALL_DEFINE0 for __arm64_sys_ni_syscall instead and
remove the now unnecessary casts.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 arch/arm64/kernel/sys.c   | 14 +++++++++-----
 arch/arm64/kernel/sys32.c | 12 ++++++++----
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/sys.c b/arch/arm64/kernel/sys.c
index b44065fb16160..4f8e8a7237a85 100644
--- a/arch/arm64/kernel/sys.c
+++ b/arch/arm64/kernel/sys.c
@@ -47,22 +47,26 @@ SYSCALL_DEFINE1(arm64_personality, unsigned int, personality)
 	return ksys_personality(personality);
 }
 
+asmlinkage long sys_ni_syscall(void);
+
+SYSCALL_DEFINE0(ni_syscall)
+{
+	return sys_ni_syscall();
+}
+
 /*
  * Wrappers to pass the pt_regs argument.
  */
 #define sys_personality		sys_arm64_personality
 
-asmlinkage long sys_ni_syscall(const struct pt_regs *);
-#define __arm64_sys_ni_syscall	sys_ni_syscall
-
 #undef __SYSCALL
 #define __SYSCALL(nr, sym)	asmlinkage long __arm64_##sym(const struct pt_regs *);
 #include <asm/unistd.h>
 
 #undef __SYSCALL
-#define __SYSCALL(nr, sym)	[nr] = (syscall_fn_t)__arm64_##sym,
+#define __SYSCALL(nr, sym)	[nr] = __arm64_##sym,
 
 const syscall_fn_t sys_call_table[__NR_syscalls] = {
-	[0 ... __NR_syscalls - 1] = (syscall_fn_t)sys_ni_syscall,
+	[0 ... __NR_syscalls - 1] = __arm64_sys_ni_syscall,
 #include <asm/unistd.h>
 };
diff --git a/arch/arm64/kernel/sys32.c b/arch/arm64/kernel/sys32.c
index 0f8bcb7de7008..f8f6c26cfd326 100644
--- a/arch/arm64/kernel/sys32.c
+++ b/arch/arm64/kernel/sys32.c
@@ -133,17 +133,21 @@ COMPAT_SYSCALL_DEFINE6(aarch32_fallocate, int, fd, int, mode,
 	return ksys_fallocate(fd, mode, arg_u64(offset), arg_u64(len));
 }
 
-asmlinkage long sys_ni_syscall(const struct pt_regs *);
-#define __arm64_sys_ni_syscall	sys_ni_syscall
+asmlinkage long sys_ni_syscall(void);
+
+COMPAT_SYSCALL_DEFINE0(ni_syscall)
+{
+	return sys_ni_syscall();
+}
 
 #undef __SYSCALL
 #define __SYSCALL(nr, sym)	asmlinkage long __arm64_##sym(const struct pt_regs *);
 #include <asm/unistd32.h>
 
 #undef __SYSCALL
-#define __SYSCALL(nr, sym)	[nr] = (syscall_fn_t)__arm64_##sym,
+#define __SYSCALL(nr, sym)	[nr] = __arm64_##sym,
 
 const syscall_fn_t compat_sys_call_table[__NR_compat_syscalls] = {
-	[0 ... __NR_compat_syscalls - 1] = (syscall_fn_t)sys_ni_syscall,
+	[0 ... __NR_compat_syscalls - 1] = __arm64_sys_ni_syscall,
 #include <asm/unistd32.h>
 };
-- 
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Re: [PATCH v2 3/3] arm64: use the correct function type for __arm64_sys_ni_syscall

[Mark Rutland]

On Fri, May 03, 2019 at 12:12:25PM -0700, Sami Tolvanen wrote:
> Calling sys_ni_syscall through a syscall_fn_t pointer trips indirect
> call Control-Flow Integrity checking due to a function type
> mismatch. Use SYSCALL_DEFINE0 for __arm64_sys_ni_syscall instead and
> remove the now unnecessary casts.
> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  arch/arm64/kernel/sys.c   | 14 +++++++++-----
>  arch/arm64/kernel/sys32.c | 12 ++++++++----
>  2 files changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm64/kernel/sys.c b/arch/arm64/kernel/sys.c
> index b44065fb16160..4f8e8a7237a85 100644
> --- a/arch/arm64/kernel/sys.c
> +++ b/arch/arm64/kernel/sys.c
> @@ -47,22 +47,26 @@ SYSCALL_DEFINE1(arm64_personality, unsigned int, personality)
>  	return ksys_personality(personality);
>  }
>  
> +asmlinkage long sys_ni_syscall(void);
> +
> +SYSCALL_DEFINE0(ni_syscall)
> +{
> +	return sys_ni_syscall();
> +}

I strongly think that we cant to fix up the common definition in
kernel/sys_ni.c rather than having a point-hack in arm64. Other
architectures (e.g. x86, s390) will want the same for CFI, and I'd like
to ensure that our approached don't diverge.

I took a quick look, and it looks like it's messy but possible to fix
up the core.

I also suspect that using SYSCALL_DEFINE0() as it currently stands isn't
a great idea, since it'll allow fault injection for unimplemented
syscalls, which sounds dubious to me.

Thanks,
Mark.

> +
>  /*
>   * Wrappers to pass the pt_regs argument.
>   */
>  #define sys_personality		sys_arm64_personality
>  
> -asmlinkage long sys_ni_syscall(const struct pt_regs *);
> -#define __arm64_sys_ni_syscall	sys_ni_syscall
> -
>  #undef __SYSCALL
>  #define __SYSCALL(nr, sym)	asmlinkage long __arm64_##sym(const struct pt_regs *);
>  #include <asm/unistd.h>
>  
>  #undef __SYSCALL
> -#define __SYSCALL(nr, sym)	[nr] = (syscall_fn_t)__arm64_##sym,
> +#define __SYSCALL(nr, sym)	[nr] = __arm64_##sym,
>  
>  const syscall_fn_t sys_call_table[__NR_syscalls] = {
> -	[0 ... __NR_syscalls - 1] = (syscall_fn_t)sys_ni_syscall,
> +	[0 ... __NR_syscalls - 1] = __arm64_sys_ni_syscall,
>  #include <asm/unistd.h>
>  };
> diff --git a/arch/arm64/kernel/sys32.c b/arch/arm64/kernel/sys32.c
> index 0f8bcb7de7008..f8f6c26cfd326 100644
> --- a/arch/arm64/kernel/sys32.c
> +++ b/arch/arm64/kernel/sys32.c
> @@ -133,17 +133,21 @@ COMPAT_SYSCALL_DEFINE6(aarch32_fallocate, int, fd, int, mode,
>  	return ksys_fallocate(fd, mode, arg_u64(offset), arg_u64(len));
>  }
>  
> -asmlinkage long sys_ni_syscall(const struct pt_regs *);
> -#define __arm64_sys_ni_syscall	sys_ni_syscall
> +asmlinkage long sys_ni_syscall(void);
> +
> +COMPAT_SYSCALL_DEFINE0(ni_syscall)
> +{
> +	return sys_ni_syscall();
> +}
>  
>  #undef __SYSCALL
>  #define __SYSCALL(nr, sym)	asmlinkage long __arm64_##sym(const struct pt_regs *);
>  #include <asm/unistd32.h>
>  
>  #undef __SYSCALL
> -#define __SYSCALL(nr, sym)	[nr] = (syscall_fn_t)__arm64_##sym,
> +#define __SYSCALL(nr, sym)	[nr] = __arm64_##sym,
>  
>  const syscall_fn_t compat_sys_call_table[__NR_compat_syscalls] = {
> -	[0 ... __NR_compat_syscalls - 1] = (syscall_fn_t)sys_ni_syscall,
> +	[0 ... __NR_compat_syscalls - 1] = __arm64_sys_ni_syscall,
>  #include <asm/unistd32.h>
>  };
> -- 
> 2.21.0.1020.gf2820cf01a-goog
> 

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Re: [PATCH v2 3/3] arm64: use the correct function type for __arm64_sys_ni_syscall

[Sami Tolvanen]

On Tue, May 07, 2019 at 06:25:12PM +0100, Mark Rutland wrote:
> I strongly think that we cant to fix up the common definition in
> kernel/sys_ni.c rather than having a point-hack in arm64. Other
> architectures (e.g. x86, s390) will want the same for CFI, and I'd like
> to ensure that our approached don't diverge.

s390 already has the following in arch/s390/kernel/sys_s390.c:

  SYSCALL_DEFINE0(ni_syscall)
  {
        return -ENOSYS;
  }

Which, I suppose, is cleaner than calling sys_ni_syscall.

> I took a quick look, and it looks like it's messy but possible to fix
> up the core.

OK. How would you propose fixing this?

Sami

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Re: [PATCH v2 3/3] arm64: use the correct function type for __arm64_sys_ni_syscall

[Will Deacon]

On Tue, May 07, 2019 at 11:32:27AM -0700, Sami Tolvanen wrote:
> On Tue, May 07, 2019 at 06:25:12PM +0100, Mark Rutland wrote:
> > I strongly think that we cant to fix up the common definition in
> > kernel/sys_ni.c rather than having a point-hack in arm64. Other
> > architectures (e.g. x86, s390) will want the same for CFI, and I'd like
> > to ensure that our approached don't diverge.
> 
> s390 already has the following in arch/s390/kernel/sys_s390.c:
> 
>   SYSCALL_DEFINE0(ni_syscall)
>   {
>         return -ENOSYS;
>   }
> 
> Which, I suppose, is cleaner than calling sys_ni_syscall.
> 
> > I took a quick look, and it looks like it's messy but possible to fix
> > up the core.
> 
> OK. How would you propose fixing this?

In the absence of a patch from Mark, I'd suggest just adding a SYS_NI macro
to our asm/syscall_wrapper.h file which avoids the error injection stuff. It
doesn't preclude moving this to the core later on, but it unblocks the CFI
work.

Will

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Re: [PATCH v2 3/3] arm64: use the correct function type for __arm64_sys_ni_syscall

[Will Deacon]

Hi Sami,

On Wed, May 15, 2019 at 12:40:39PM +0100, Will Deacon wrote:
> On Tue, May 07, 2019 at 11:32:27AM -0700, Sami Tolvanen wrote:
> > On Tue, May 07, 2019 at 06:25:12PM +0100, Mark Rutland wrote:
> > > I strongly think that we cant to fix up the common definition in
> > > kernel/sys_ni.c rather than having a point-hack in arm64. Other
> > > architectures (e.g. x86, s390) will want the same for CFI, and I'd like
> > > to ensure that our approached don't diverge.
> > 
> > s390 already has the following in arch/s390/kernel/sys_s390.c:
> > 
> >   SYSCALL_DEFINE0(ni_syscall)
> >   {
> >         return -ENOSYS;
> >   }
> > 
> > Which, I suppose, is cleaner than calling sys_ni_syscall.
> > 
> > > I took a quick look, and it looks like it's messy but possible to fix
> > > up the core.
> > 
> > OK. How would you propose fixing this?
> 
> In the absence of a patch from Mark, I'd suggest just adding a SYS_NI macro
> to our asm/syscall_wrapper.h file which avoids the error injection stuff. It
> doesn't preclude moving this to the core later on, but it unblocks the CFI
> work.

Do you plan to repost this?

Will

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Re: [PATCH v2 3/3] arm64: use the correct function type for __arm64_sys_ni_syscall

[Sami Tolvanen]

On Fri, May 24, 2019 at 07:35:51PM +0100, Will Deacon wrote:
> > In the absence of a patch from Mark, I'd suggest just adding a SYS_NI macro
> > to our asm/syscall_wrapper.h file which avoids the error injection stuff.

If we don't want to use SYSCALL_DEFINE0, I don't think we need a macro
at all. I believe it's cleaner to just define __arm64_sys_ni_syscall with
the correct type in sys.c.

> Do you plan to repost this?

Yes. Sorry for the delay. I'll post v3 shortly.

Sami

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