powerpc: Fix __clear_user() with KUAP enabled

The KUAP implementation adds calls in clear_user() to enable and
disable access to userspace memory. However, it doesn't add these to
__clear_user(), which is used in the ptrace regset code.

As there's only one direct user of __clear_user() (the regset code),
and the time taken to set the AMR for KUAP purposes is going to
dominate the cost of a quick access_ok(), there's not much point
having a separate path.

Rename __clear_user() to __arch_clear_user(), and make __clear_user()
just call clear_user().

Reported-by: syzbot+f25ecf4b2982d8c7a640@syzkaller-ppc64.appspotmail.com
Reported-by: Daniel Axtens <dja@axtens.net>
Suggested-by: Michael Ellerman <mpe@ellerman.id.au>
Fixes: de78a9c42a79 ("powerpc: Add a framework for Kernel Userspace Access Protection")
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
[mpe: Use __arch_clear_user() for the asm version like arm64 & nds32]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191209132221.15328-1-ajd@linux.ibm.com

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 15002b5..c92fe7f 100644 (file)
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -401,7 +401,7 @@ copy_to_user_mcsafe(void __user *to, const void *from, unsigned long n)
        return n;
 }
 
-extern unsigned long __clear_user(void __user *addr, unsigned long size);
+unsigned long __arch_clear_user(void __user *addr, unsigned long size);
 
 static inline unsigned long clear_user(void __user *addr, unsigned long size)
 {
@@ -409,12 +409,17 @@ static inline unsigned long clear_user(void __user *addr, unsigned long size)
        might_fault();
        if (likely(access_ok(addr, size))) {
                allow_write_to_user(addr, size);
-               ret = __clear_user(addr, size);
+               ret = __arch_clear_user(addr, size);
                prevent_write_to_user(addr, size);
        }
        return ret;
 }
 
+static inline unsigned long __clear_user(void __user *addr, unsigned long size)
+{
+       return clear_user(addr, size);
+}
+
 extern long strncpy_from_user(char *dst, const char __user *src, long count);
 extern __must_check long strnlen_user(const char __user *str, long n);
 

diff --git a/arch/powerpc/lib/string_32.S b/arch/powerpc/lib/string_32.S
index f69a6aa..1ddb263 100644 (file)
--- a/arch/powerpc/lib/string_32.S
+++ b/arch/powerpc/lib/string_32.S
@@ -17,7 +17,7 @@ CACHELINE_BYTES = L1_CACHE_BYTES
 LG_CACHELINE_BYTES = L1_CACHE_SHIFT
 CACHELINE_MASK = (L1_CACHE_BYTES-1)
 
-_GLOBAL(__clear_user)
+_GLOBAL(__arch_clear_user)
 /*
  * Use dcbz on the complete cache lines in the destination
  * to set them to zero.  This requires that the destination
@@ -87,4 +87,4 @@ _GLOBAL(__clear_user)
        EX_TABLE(8b, 91b)
        EX_TABLE(9b, 91b)
 
-EXPORT_SYMBOL(__clear_user)
+EXPORT_SYMBOL(__arch_clear_user)

diff --git a/arch/powerpc/lib/string_64.S b/arch/powerpc/lib/string_64.S
index 507b18b..169872b 100644 (file)
--- a/arch/powerpc/lib/string_64.S
+++ b/arch/powerpc/lib/string_64.S
@@ -17,7 +17,7 @@ PPC64_CACHES:
        .section        ".text"
 
 /**
- * __clear_user: - Zero a block of memory in user space, with less checking.
+ * __arch_clear_user: - Zero a block of memory in user space, with less checking.
  * @to:   Destination address, in user space.
  * @n:    Number of bytes to zero.
  *
@@ -58,7 +58,7 @@ err3; stb     r0,0(r3)
        mr      r3,r4
        blr
 
-_GLOBAL_TOC(__clear_user)
+_GLOBAL_TOC(__arch_clear_user)
        cmpdi   r4,32
        neg     r6,r3
        li      r0,0
@@ -181,4 +181,4 @@ err1;       dcbz    0,r3
        cmpdi   r4,32
        blt     .Lshort_clear
        b       .Lmedium_clear
-EXPORT_SYMBOL(__clear_user)
+EXPORT_SYMBOL(__arch_clear_user)