Commit 214f0e80 authored Oct 03, 2020 by Gabriel Krisman Bertazi Committed by Thomas Gleixner Oct 26, 2020

x86/compat: Simplify compat syscall userspace allocation

When allocating user memory space for a compat system call, don't consider
whether the originating code is IA32 or X32, just allocate from a safe
region for both, beyond the redzone. This should be safe for IA32, and has
the benefit of avoiding TIF_IA32, which is about to be removed.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201004032536.1229030-3-krisman@collabora.com

parent 375d4bfd

arch/x86/include/asm/compat.h

+7 −8

Original line number	Diff line number	Diff line
		@@ -177,14 +177,13 @@ typedef struct user_regs_struct compat_elf_gregset_t;

		static inline void __user *arch_compat_alloc_user_space(long len)
		{
		compat_uptr_t sp;
		compat_uptr_t sp = task_pt_regs(current)->sp;

		if (test_thread_flag(TIF_IA32)) {
		sp = task_pt_regs(current)->sp;
		} else {
		/* -128 for the x32 ABI redzone */
		sp = task_pt_regs(current)->sp - 128;
		}
		/*
		* -128 for the x32 ABI redzone. For IA32, it is not strictly
		* necessary, but not harmful.
		*/
		sp -= 128;

		return (void __user *)round_down(sp - len, 16);
		}