On March 21, 2017 9:37:12 AM PDT, Dmitry Safonov <dsafonov@xxxxxxxxxxxxx> wrote:
>After my changes to mmap(), its code now relies on the bitness of
>performing syscall. According to that, it chooses the base of
>allocation:
>mmap_base for 64-bit mmap() and mmap_compat_base for 32-bit syscall.
>It was done by:
> commit 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for
>32-bit mmap()").
>
>The code afterwards relies on in_compat_syscall() returning true for
>32-bit syscalls. It's usually so while we're in context of application
>that does 32-bit syscalls. But during exec() it is not valid for x32
>ELF.
>The reason is that the application hasn't yet done any syscall, so x32
>bit has not being set.
>That results in -ENOMEM for x32 ELF files as there fired BAD_ADDR()
>in elf_map(), that is called from do_execve()->load_elf_binary().
>For i386 ELFs it works as SET_PERSONALITY() sets TS_COMPAT flag.
>
>I suggest to set x32 bit before first return to userspace, during
>setting personality at exec(). This way we can rely on
>in_compat_syscall() during exec().
>
>Fixes: commit 1b028f784e8c ("x86/mm: Introduce mmap_compat_base() for
>32-bit mmap()")
>Cc: 0x7f454c46@xxxxxxxxx
>Cc: linux-mm@xxxxxxxxx
>Cc: Andrei Vagin <avagin@xxxxxxxxx>
>Cc: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
>Cc: Borislav Petkov <bp@xxxxxxx>
>Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
>Cc: x86@xxxxxxxxxx
>Cc: H. Peter Anvin <hpa@xxxxxxxxx>
>Cc: Andy Lutomirski <luto@xxxxxxxxxx>
>Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>Reported-by: Adam Borowski <kilobyte@xxxxxxxxxx>
>Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
>---
>v2:
>- specifying mmap() allocation path which failed during exec()
>- fix comment style
>
> arch/x86/kernel/process_64.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
>diff --git a/arch/x86/kernel/process_64.c
>b/arch/x86/kernel/process_64.c
>index d6b784a5520d..d3d4d9abcaf8 100644
>--- a/arch/x86/kernel/process_64.c
>+++ b/arch/x86/kernel/process_64.c
>@@ -519,8 +519,14 @@ void set_personality_ia32(bool x32)
> if (current->mm)
> current->mm->context.ia32_compat = TIF_X32;
> current->personality &= ~READ_IMPLIES_EXEC;
>- /* in_compat_syscall() uses the presence of the x32
>- syscall bit flag to determine compat status */
>+ /*
>+ * in_compat_syscall() uses the presence of the x32
>+ * syscall bit flag to determine compat status.
>+ * On the bitness of syscall relies x86 mmap() code,
>+ * so set x32 syscall bit right here to make
>+ * in_compat_syscall() work during exec().
>+ */
>+ task_pt_regs(current)->orig_ax |= __X32_SYSCALL_BIT;
> current->thread.status &= ~TS_COMPAT;
> } else {
> set_thread_flag(TIF_IA32);
You also need to clear the bit for an x32 -> x86-64 exec. Otherwise it seems okay to me.
--
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