[RFC6 PATCH v6 00/21] ILP32 for ARM64
From: catalin.marinas@arm.com (Catalin Marinas)
Date: 2016-05-12 13:35:42
Also in:
linux-arch, linux-s390, lkml
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.
quoted hunk ↗ jump to hunk
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.
quoted hunk ↗ jump to hunk
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.
quoted hunk ↗ jump to hunk
#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_DLINFOdiff --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. -- Catalin