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Subject[PATCH 2/6] x86: Simplify compat syscall userspace allocation
Date
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 we want to drop.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
arch/x86/include/asm/compat.h | 15 +++++++--------
1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/compat.h b/arch/x86/include/asm/compat.h
index d4edf281fff4..a4b5126dff4e 100644
--- a/arch/x86/include/asm/compat.h
+++ b/arch/x86/include/asm/compat.h
@@ -179,14 +179,13 @@ typedef struct user_regs_struct compat_elf_gregset_t;

static inline void __user *arch_compat_alloc_user_space(long len)
{
- compat_uptr_t sp;
-
- 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;
- }
+ compat_uptr_t sp = task_pt_regs(current)->sp;
+
+ /*
+ * -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);
}
--
2.28.0
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