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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
This commit is contained in:
Gabriel Krisman Bertazi 2020-10-03 23:25:28 -04:00 committed by Thomas Gleixner
parent 375d4bfda5
commit 214f0e8043
1 changed files with 6 additions and 7 deletions
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13
arch/x86/include/asm/compat.h
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@ -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);
}