On Thu, Apr 02, 2020 at 07:34:16AM +0000, Christophe Leroy wrote: > Some architectures like powerpc64 have the capability to separate > read access and write access protection. > For get_user() and copy_from_user(), powerpc64 only open read access. > For put_user() and copy_to_user(), powerpc64 only open write access. > But when using unsafe_get_user() or unsafe_put_user(), > user_access_begin open both read and write. > > Other architectures like powerpc book3s 32 bits only allow write > access protection. And on this architecture protection is an heavy > operation as it requires locking/unlocking per segment of 256Mbytes. > On those architecture it is therefore desirable to do the unlocking > only for write access. (Note that book3s/32 ranges from very old > powermac from the 90's with powerpc 601 processor, till modern > ADSL boxes with PowerQuicc II modern processors for instance so it > is still worth considering) > > In order to avoid any risk based of hacking some variable parameters > passed to user_access_begin/end that would allow hacking and > leaving user access open or opening too much, it is preferable to > use dedicated static functions that can't be overridden. > > Add a user_read_access_begin and user_read_access_end to only open > read access. > > Add a user_write_access_begin and user_write_access_end to only open > write access. > > By default, when undefined, those new access helpers default on the > existing user_access_begin and user_access_end. > > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> -Kees > Link: https://patchwork.ozlabs.org/patch/1227926/ > --- > Resending this series as I mistakenly only sent it to powerpc list > begining of February (https://patchwork.ozlabs.org/patch/1233172/) > > This series is based on the discussion we had in January, see > https://patchwork.ozlabs.org/patch/1227926/ . I tried to > take into account all remarks, especially @hpa 's remark to use > a fixed API on not base the relocking on a magic id returned at > unlocking. > > This series is awaited for implementing selective lkdtm test to > test powerpc64 independant read and write protection, see > https://patchwork.ozlabs.org/patch/1231765/ > > include/linux/uaccess.h | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h > index 67f016010aad..9861c89f93be 100644 > --- a/include/linux/uaccess.h > +++ b/include/linux/uaccess.h > @@ -378,6 +378,14 @@ extern long strnlen_unsafe_user(const void __user *unsafe_addr, long count); > static inline unsigned long user_access_save(void) { return 0UL; } > static inline void user_access_restore(unsigned long flags) { } > #endif > +#ifndef user_write_access_begin > +#define user_write_access_begin user_access_begin > +#define user_write_access_end user_access_end > +#endif > +#ifndef user_read_access_begin > +#define user_read_access_begin user_access_begin > +#define user_read_access_end user_access_end > +#endif > > #ifdef CONFIG_HARDENED_USERCOPY > void usercopy_warn(const char *name, const char *detail, bool to_user, > -- > 2.25.0 > -- Kees Cook
