Re: [PATCH 06/11] powerpc: Use orig_gpr3 in syscall_get_arguments()

2015-07-27 Thread Kees Cook 
On Thu, Jul 23, 2015 at 3:21 AM, Michael Ellerman m...@ellerman.id.au wrote:
 Currently syscall_get_arguments() is used by syscall tracepoints, and
 collect_syscall() which is used in some debugging as well as
 /proc/pid/syscall.

 The current implementation just copies regs-gpr[3 .. 5] out, which is
 fine for all the current use cases.

 When we enable seccomp filter, that will also start using
 syscall_get_arguments(). However for seccomp filter we want to use r3
 as the return value of the syscall, and orig_gpr3 as the first
 parameter. This will allow seccomp to modify the return value in r3.

 To support this we need to modify syscall_get_arguments() to return
 orig_gpr3 instead of r3. This is safe for all uses because orig_gpr3
 always contains the r3 value that was passed to the syscall. We store it
 in the syscall entry path and never modify it.

 Update syscall_set_arguments() while we're here, even though it's never
 used.

 Signed-off-by: Michael Ellerman m...@ellerman.id.au

Reviewed-by: Kees Cook keesc...@chromium.org

-Kees

 ---
  arch/powerpc/include/asm/syscall.h | 16 +---
  1 file changed, 13 insertions(+), 3 deletions(-)

 diff --git a/arch/powerpc/include/asm/syscall.h 
 b/arch/powerpc/include/asm/syscall.h
 index 403e2303fe18..8d79a87c0511 100644
 --- a/arch/powerpc/include/asm/syscall.h
 +++ b/arch/powerpc/include/asm/syscall.h
 @@ -64,7 +64,7 @@ static inline void syscall_get_arguments(struct task_struct 
 *task,
  unsigned int i, unsigned int n,
  unsigned long *args)
  {
 -   unsigned long mask = -1UL;
 +   unsigned long val, mask = -1UL;

 BUG_ON(i + n  6);

 @@ -72,8 +72,14 @@ static inline void syscall_get_arguments(struct 
 task_struct *task,
 if (test_tsk_thread_flag(task, TIF_32BIT))
 mask = 0x;
  #endif
 -   while (n--)
 -   args[n] = regs-gpr[3 + i + n]  mask;
 +   while (n--) {
 +   if (n == 0  i == 0)
 +   val = regs-orig_gpr3;
 +   else
 +   val = regs-gpr[3 + i + n];
 +
 +   args[n] = val  mask;
 +   }
  }

  static inline void syscall_set_arguments(struct task_struct *task,
 @@ -83,6 +89,10 @@ static inline void syscall_set_arguments(struct 
 task_struct *task,
  {
 BUG_ON(i + n  6);
 memcpy(regs-gpr[3 + i], args, n * sizeof(args[0]));
 +
 +   /* Also copy the first argument into orig_gpr3 */
 +   if (i == 0  n  0)
 +   regs-orig_gpr3 = args[0];
  }

  static inline int syscall_get_arch(void)
 --
 2.1.0




-- 
Kees Cook
Chrome OS Security
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[PATCH 06/11] powerpc: Use orig_gpr3 in syscall_get_arguments()

2015-07-23 Thread Michael Ellerman 
Currently syscall_get_arguments() is used by syscall tracepoints, and
collect_syscall() which is used in some debugging as well as
/proc/pid/syscall.

The current implementation just copies regs-gpr[3 .. 5] out, which is
fine for all the current use cases.

When we enable seccomp filter, that will also start using
syscall_get_arguments(). However for seccomp filter we want to use r3
as the return value of the syscall, and orig_gpr3 as the first
parameter. This will allow seccomp to modify the return value in r3.

To support this we need to modify syscall_get_arguments() to return
orig_gpr3 instead of r3. This is safe for all uses because orig_gpr3
always contains the r3 value that was passed to the syscall. We store it
in the syscall entry path and never modify it.

Update syscall_set_arguments() while we're here, even though it's never
used.

Signed-off-by: Michael Ellerman m...@ellerman.id.au
---
 arch/powerpc/include/asm/syscall.h | 16 +---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/syscall.h 
b/arch/powerpc/include/asm/syscall.h
index 403e2303fe18..8d79a87c0511 100644
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h
@@ -64,7 +64,7 @@ static inline void syscall_get_arguments(struct task_struct 
*task,
 unsigned int i, unsigned int n,
 unsigned long *args)
 {
-   unsigned long mask = -1UL;
+   unsigned long val, mask = -1UL;
 
BUG_ON(i + n  6);
 
@@ -72,8 +72,14 @@ static inline void syscall_get_arguments(struct task_struct 
*task,
if (test_tsk_thread_flag(task, TIF_32BIT))
mask = 0x;
 #endif
-   while (n--)
-   args[n] = regs-gpr[3 + i + n]  mask;
+   while (n--) {
+   if (n == 0  i == 0)
+   val = regs-orig_gpr3;
+   else
+   val = regs-gpr[3 + i + n];
+
+   args[n] = val  mask;
+   }
 }
 
 static inline void syscall_set_arguments(struct task_struct *task,
@@ -83,6 +89,10 @@ static inline void syscall_set_arguments(struct task_struct 
*task,
 {
BUG_ON(i + n  6);
memcpy(regs-gpr[3 + i], args, n * sizeof(args[0]));
+
+   /* Also copy the first argument into orig_gpr3 */
+   if (i == 0  n  0)
+   regs-orig_gpr3 = args[0];
 }
 
 static inline int syscall_get_arch(void)
-- 
2.1.0

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