On Thu, May 12, 2016 at 02:35:34PM +0100, Catalin Marinas wrote: > On Thu, May 12, 2016 at 03:20:00AM +0300, Yury Norov wrote: > > I debugged preadv02 and pwritev02 failures and found very weird bug. > > Test passes {iovec_base = 0xffffffff, iovec_len = 64} as one element > > of vector, and kernel reports successful read/write. > > > > There are 2 problems: > > 1. How kernel allows such address to be passed to fs subsystem; > > 2. How fs successes to read/write at non-mapped, and in fact non-user > > address. > > > > I don't know the answer on 2'nd question, and it might be something > > generic. But I investigated first problem. > > > > The problem is that compat_rw_copy_check_uvector() uses access_ok() to > > validate user address, and on arm64 it ends up with checking buffer > > end against current_thread_info()->addr_limit. > > > > current_thread_info()->addr_limit for ilp32, and most probably for > > aarch32 is equal to aarch64 one, and so adress_ok() doesn't fail. > > It happens because on thread creation we call flush_old_exec() to set > > addr_limit, and completely ignore compat mode there. > > I assume accesses beyond this address would fault anyway but I haven't > checked the code paths. > > > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h > > index 7a39683..6ba4952 100644 > > --- a/arch/arm64/include/asm/elf.h > > +++ b/arch/arm64/include/asm/elf.h > > @@ -146,6 +146,7 @@ typedef struct user_fpsimd_state elf_fpregset_t; > > do { \ > > clear_thread_flag(TIF_32BIT_AARCH64); \ > > clear_thread_flag(TIF_32BIT); \ > > + set_fs(TASK_SIZE_64); \ > > } while (0) > > See below. > > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h > > index 19cfdc5..3b0dd8d 100644 > > --- a/arch/arm64/include/asm/uaccess.h > > +++ b/arch/arm64/include/asm/uaccess.h > > @@ -51,7 +51,7 @@ > > #define KERNEL_DS (-1UL) > > #define get_ds() (KERNEL_DS) > > > > -#define USER_DS TASK_SIZE_64 > > +#define USER_DS TASK_SIZE > > I agree with this. > > > #define get_fs() (current_thread_info()->addr_limit) > > > > static inline void set_fs(mm_segment_t fs) > > diff --git a/arch/arm64/kernel/binfmt_elf32.c b/arch/arm64/kernel/binfmt_elf32.c > > index 5487872..2e8d9f3 100644 > > --- a/arch/arm64/kernel/binfmt_elf32.c > > +++ b/arch/arm64/kernel/binfmt_elf32.c > > @@ -12,6 +12,7 @@ > > do { \ > > clear_thread_flag(TIF_32BIT_AARCH64); \ > > set_thread_flag(TIF_32BIT); \ > > + set_fs(TASK_SIZE_32); \ > > } while (0) > > > > #define COMPAT_ARCH_DLINFO > > diff --git a/arch/arm64/kernel/binfmt_ilp32.c b/arch/arm64/kernel/binfmt_ilp32.c > > index a934fd4..a8599c6 100644 > > --- a/arch/arm64/kernel/binfmt_ilp32.c > > +++ b/arch/arm64/kernel/binfmt_ilp32.c > > @@ -59,6 +59,7 @@ static void cputime_to_compat_timeval(const cputime_t cputime, > > do { \ > > set_thread_flag(TIF_32BIT_AARCH64); \ > > clear_thread_flag(TIF_32BIT); \ > > + set_fs(TASK_SIZE_32); \ > > } while (0) > > I don't think we need these two. AFAICT, flush_old_exec() takes care of > setting the USER_DS for the new thread. That's true, but USER_DS depends on personality which is not set yet for new thread, as I wrote above. In fact, I tried correct USER_DS only, and it doesn't work > > -- > Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html