From: Will Deacon Date: Mon, 2 Jun 2014 10:47:23 +0000 (+0100) Subject: arm64: ptrace: change fs when passing kernel pointer to regset code X-Git-Tag: firefly_0821_release~3680^2~30^2^2~23^2~1 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=ab7ccd91004b55c29910c999f51bc40880646810;p=firefly-linux-kernel-4.4.55.git 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 (cherry picked from commit c168870704bcde6bb63d05f7882b620dd3985a46) Signed-off-by: Mark Brown --- diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 5341534b6d04..85536688f753 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -872,6 +872,7 @@ 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; @@ -879,10 +880,13 @@ 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; }