Le 24/04/2018 à 16:50, Mathieu Malaterre a écrit :

On Tue, Apr 24, 2018 at 4:45 PM, Mathieu Malaterre [off-list ref] wrote:

quoted

On Tue, Apr 24, 2018 at 4:17 PM, Christophe Leroy
[off-list ref] wrote:

quoted

Use fault_in_pages_readable() to prefault user context
instead of open coding

Signed-off-by: Christophe Leroy <redacted>
---
  arch/powerpc/kernel/signal_32.c | 13 +++++--------
  1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/kernel/signal_32.c b/arch/powerpc/kernel/signal_32.c
index 492f03451877..cfacb2726152 100644
--- a/arch/powerpc/kernel/signal_32.c
+++ b/arch/powerpc/kernel/signal_32.c

@@ -25,6 +25,7 @@
  #include <linux/errno.h>
  #include <linux/elf.h>
  #include <linux/ptrace.h>
+#include <linux/pagemap.h>
  #include <linux/ratelimit.h>
  #ifdef CONFIG_PPC64
  #include <linux/syscalls.h>

@@ -1045,7 +1046,6 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
                      struct ucontext __user *new_ctx,
                      int ctx_size, int r6, int r7, int r8, struct pt_regs *regs)
  {
-       unsigned char tmp __maybe_unused;
         int ctx_has_vsx_region = 0;

  #ifdef CONFIG_PPC64

@@ -1109,9 +1109,8 @@ long sys_swapcontext(struct ucontext __user *old_ctx,
         }
         if (new_ctx == NULL)
                 return 0;
-       if (!access_ok(VERIFY_READ, new_ctx, ctx_size)
-           || __get_user(tmp, (u8 __user *) new_ctx)
-           || __get_user(tmp, (u8 __user *) new_ctx + ctx_size - 1))
+       if (!access_ok(VERIFY_READ, new_ctx, ctx_size) ||
+           fault_in_pages_readable((u8 __user *)new_ctx, ctx_size))
                 return -EFAULT;

         /*

@@ -1231,7 +1230,6 @@ int sys_debug_setcontext(struct ucontext __user *ctx,
  {
         struct sig_dbg_op op;
         int i;
-       unsigned char tmp __maybe_unused;
         unsigned long new_msr = regs->msr;
  #ifdef CONFIG_PPC_ADV_DEBUG_REGS
         unsigned long new_dbcr0 = current->thread.debug.dbcr0;

@@ -1287,9 +1285,8 @@ int sys_debug_setcontext(struct ucontext __user *ctx,
         current->thread.debug.dbcr0 = new_dbcr0;
  #endif

-       if (!access_ok(VERIFY_READ, ctx, sizeof(*ctx))
-           || __get_user(tmp, (u8 __user *) ctx)
-           || __get_user(tmp, (u8 __user *) (ctx + 1) - 1))
+       if (!access_ok(VERIFY_READ, ctx, sizeof(*ctx)) ||
+           fault_in_pages_readable((u8 __user *)ctx, 1))

I believe you meant:

fault_in_pages_readable((u8 __user *)new_ctx, ctx_size)

Since (u8 __user *) (ctx + 1) - 1 really is (u8 __user *) new_ctx + ctx_size - 1

Without the copy/paste errors:

[...]
fault_in_pages_readable((u8 __user *)ctx, sizeof(*ctx))

Since (u8 __user *) (ctx + 1) - 1 really is (u8 __user *) ctx + sizeof(*ctx) - 1
[...]

Oops you're right thanks.
v2 submitted

Christophe

quoted

quoted

                 return -EFAULT;

         /*
--
2.13.3