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    Subject[PATCH 4.9 06/16] powerpc: Fix __clear_user() with KUAP enabled
    Date
    From: Andrew Donnellan <ajd@linux.ibm.com>

    commit 61e3acd8c693a14fc69b824cb5b08d02cb90a6e7 upstream.

    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
    Signed-off-by: Daniel Axtens <dja@axtens.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/powerpc/include/asm/uaccess.h | 9 +++++++--
    arch/powerpc/lib/string.S | 4 ++--
    arch/powerpc/lib/string_64.S | 6 +++---
    3 files changed, 12 insertions(+), 7 deletions(-)

    --- a/arch/powerpc/include/asm/uaccess.h
    +++ b/arch/powerpc/include/asm/uaccess.h
    @@ -460,7 +460,7 @@ static inline unsigned long __copy_to_us
    return __copy_to_user_inatomic(to, from, size);
    }

    -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)
    {
    @@ -468,12 +468,17 @@ static inline unsigned long clear_user(v
    might_fault();
    if (likely(access_ok(VERIFY_WRITE, 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 strlen_user(const char __user *str);
    extern __must_check long strnlen_user(const char __user *str, long n);
    --- a/arch/powerpc/lib/string.S
    +++ b/arch/powerpc/lib/string.S
    @@ -89,7 +89,7 @@ _GLOBAL(memchr)
    EXPORT_SYMBOL(memchr)

    #ifdef CONFIG_PPC32
    -_GLOBAL(__clear_user)
    +_GLOBAL(__arch_clear_user)
    addi r6,r3,-4
    li r3,0
    li r5,0
    @@ -130,5 +130,5 @@ _GLOBAL(__clear_user)
    PPC_LONG 1b,91b
    PPC_LONG 8b,92b
    .text
    -EXPORT_SYMBOL(__clear_user)
    +EXPORT_SYMBOL(__arch_clear_user)
    #endif
    --- a/arch/powerpc/lib/string_64.S
    +++ b/arch/powerpc/lib/string_64.S
    @@ -28,7 +28,7 @@ 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.
    *
    @@ -78,7 +78,7 @@ 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
    @@ -201,4 +201,4 @@ err1; dcbz 0,r3
    cmpdi r4,32
    blt .Lshort_clear
    b .Lmedium_clear
    -EXPORT_SYMBOL(__clear_user)
    +EXPORT_SYMBOL(__arch_clear_user)

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