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powerpc: Fix __clear_user() with KUAP enabled

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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: de78a9c42a ("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
This commit is contained in:
Andrew Donnellan
2019-12-10 00:22:21 +11:00
committed by Michael Ellerman
parent e352f576d3
commit 61e3acd8c6
3 changed files with 12 additions and 7 deletions
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9
arch/powerpc/include/asm/uaccess.h
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@@ -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);