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    SubjectRe: [PATCH v17 02/15] lib, arm64: untag user pointers in strn*_user
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    On 12/06/2019 12:43, Andrey Konovalov wrote:
    > This patch is a part of a series that extends arm64 kernel ABI to allow to
    > pass tagged user pointers (with the top byte set to something else other
    > than 0x00) as syscall arguments.
    >
    > strncpy_from_user and strnlen_user accept user addresses as arguments, and
    > do not go through the same path as copy_from_user and others, so here we
    > need to handle the case of tagged user addresses separately.
    >
    > Untag user pointers passed to these functions.
    >
    > Note, that this patch only temporarily untags the pointers to perform
    > validity checks, but then uses them as is to perform user memory accesses.
    >
    > Reviewed-by: Khalid Aziz <khalid.aziz@oracle.com>
    > Acked-by: Kees Cook <keescook@chromium.org>
    > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
    > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

    Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

    > ---
    > lib/strncpy_from_user.c | 3 ++-
    > lib/strnlen_user.c | 3 ++-
    > 2 files changed, 4 insertions(+), 2 deletions(-)
    >
    > diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
    > index 023ba9f3b99f..dccb95af6003 100644
    > --- a/lib/strncpy_from_user.c
    > +++ b/lib/strncpy_from_user.c
    > @@ -6,6 +6,7 @@
    > #include <linux/uaccess.h>
    > #include <linux/kernel.h>
    > #include <linux/errno.h>
    > +#include <linux/mm.h>
    >
    > #include <asm/byteorder.h>
    > #include <asm/word-at-a-time.h>
    > @@ -108,7 +109,7 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
    > return 0;
    >
    > max_addr = user_addr_max();
    > - src_addr = (unsigned long)src;
    > + src_addr = (unsigned long)untagged_addr(src);
    > if (likely(src_addr < max_addr)) {
    > unsigned long max = max_addr - src_addr;
    > long retval;
    > diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
    > index 7f2db3fe311f..28ff554a1be8 100644
    > --- a/lib/strnlen_user.c
    > +++ b/lib/strnlen_user.c
    > @@ -2,6 +2,7 @@
    > #include <linux/kernel.h>
    > #include <linux/export.h>
    > #include <linux/uaccess.h>
    > +#include <linux/mm.h>
    >
    > #include <asm/word-at-a-time.h>
    >
    > @@ -109,7 +110,7 @@ long strnlen_user(const char __user *str, long count)
    > return 0;
    >
    > max_addr = user_addr_max();
    > - src_addr = (unsigned long)str;
    > + src_addr = (unsigned long)untagged_addr(str);
    > if (likely(src_addr < max_addr)) {
    > unsigned long max = max_addr - src_addr;
    > long retval;
    >

    --
    Regards,
    Vincenzo

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