From c168870704bcde6bb63d05f7882b620dd3985a46 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Mon, 2 Jun 2014 11:47:23 +0100 Subject: arm64: ptrace: change fs when passing kernel pointer to regset code Our compat PTRACE_POKEUSR implementation simply passes the user data to regset_copy_from_user after some simple range checking. Unfortunately, the data in question has already been copied to the kernel stack by this point, so the subsequent access_ok check fails and the ptrace request returns -EFAULT. This causes problems tracing fork() with older versions of strace. This patch briefly changes the fs to KERNEL_DS, so that the access_ok check passes even with a kernel address. Signed-off-by: Will Deacon Cc: Signed-off-by: Catalin Marinas --- arch/arm64/kernel/ptrace.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/arm64') diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 3e926b9c0641..993cdb79b70e 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -827,6 +827,7 @@ static int compat_ptrace_write_user(struct task_struct *tsk, compat_ulong_t off, compat_ulong_t val) { int ret; + mm_segment_t old_fs = get_fs(); if (off & 3 || off >= COMPAT_USER_SZ) return -EIO; @@ -834,10 +835,13 @@ static int compat_ptrace_write_user(struct task_struct *tsk, compat_ulong_t off, if (off >= sizeof(compat_elf_gregset_t)) return 0; + set_fs(KERNEL_DS); ret = copy_regset_from_user(tsk, &user_aarch32_view, REGSET_COMPAT_GPR, off, sizeof(compat_ulong_t), &val); + set_fs(old_fs); + return ret; } -- cgit v1.2.3