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x86/mm: Make in_compat_syscall() work during exec
The x86 mmap() code selects the mmap base for an allocation depending on the bitness of the syscall. For 64bit sycalls it select mm->mmap_base and for 32bit mm->mmap_compat_base. On execve the registers of the task invoking exec() are copied to the child pt_regs. So child->pt_regs->orig_ax contains the execve syscall number of the parent. exec() calls mmap() which in turn uses in_compat_syscall() to check whether the mapping is for a 32bit or a 64bit task. The decision is made on the following criteria: ia32 child->thread.status & TS_COMPAT x32 child->pt_regs.orig_ax & __X32_SYSCALL_BIT ia64 !ia32 && !x32 child->thread.status is corretly set up in set_personality_*(), but the syscall number in child->pt_regs.orig_ax is left unmodified. Therefore the parent/child combinations work or fail in the following way: Parent Child Child->thread_status child->pt_regs.orig_ax in_compat() Works ia64 ia64 TS_COMPAT == 0 __X32_SYSCALL_BIT == 0 false Y ia64 ia32 TS_COMPAT == 1 __X32_SYSCALL_BIT == 0 true Y ia64 x32 TS_COMPAT == 0 __X32_SYSCALL_BIT == 0 false N ia32 ia64 TS_COMPAT == 0 __X32_SYSCALL_BIT == 0 false Y ia32 ia32 TS_COMPAT == 1 __X32_SYSCALL_BIT == 0 true Y ia32 x32 TS_COMPAT == 0 __X32_SYSCALL_BIT == 0 false N x32 ia64 TS_COMPAT == 0 __X32_SYSCALL_BIT == 1 true N x32 ia32 TS_COMPAT == 1 __X32_SYSCALL_BIT == 1 true Y x32 x32 TS_COMPAT == 0 __X32_SYSCALL_BIT == 1 true Y Make set_personality_*() store the syscall number incl. __X32_SYSCALL_BIT which corresponds to the newly started ELF executable in the childs pt_regs, i.e. pretend that the exec was invoked from a task with the same executable format. So both thread.status and pt_regs.orig_ax correspond to the new ELF format and in_compat_syscall() returns the correct result. [ tglx: Rewrote changelog ] Fixes: commit 1b028f78 ("x86/mm: Introduce mmap_compat_base() for 32-bit mmap()") Reported-by:Adam Borowski <kilobyte@angband.pl> Suggested-by: