From fc3e958a2b552fe6210e6de3bebb4348156a0b5f Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Sat, 4 Apr 2015 20:55:19 +0200 Subject: [PATCH] x86/asm/entry: Clear EXTRA_REGS for all executable formats On failure, sys_execve() does not clobber EXTRA_REGS, so we can just return to userpsace without saving/restoring them. On success, ELF_PLAT_INIT() in sys_execve() clears all these registers. On other executable formats: - binfmt_flat.c has similar FLAT_PLAT_INIT, but x86 (and everyone else except sh) doesn't define it. - binfmt_elf_fdpic.c has ELF_FDPIC_PLAT_INIT, but x86 (and most others) doesn't define it. - There are no such hooks in binfmt_aout.c et al. We inherit EXTRA_REGS from the prior executable. This inconsistency was not intended. This change removes SAVE/RESTORE_EXTRA_REGS in stub_execve, removes register clearing in ELF_PLAT_INIT(), and instead simply clears them on success in stub_execve. Run-tested. Signed-off-by: Denys Vlasenko Cc: Alexei Starovoitov Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Steven Rostedt Cc: Will Drewry Link: http://lkml.kernel.org/r/1428173719-7637-1-git-send-email-dvlasenk@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/include/asm/calling.h | 9 ++++++ arch/x86/include/asm/elf.h | 7 +++-- arch/x86/kernel/entry_64.S | 50 +++++++++++++++------------------- 3 files changed, 35 insertions(+), 31 deletions(-) diff --git a/arch/x86/include/asm/calling.h b/arch/x86/include/asm/calling.h index 4b5f7bf2b780..1c8b50edb2db 100644 --- a/arch/x86/include/asm/calling.h +++ b/arch/x86/include/asm/calling.h @@ -151,6 +151,15 @@ For 32-bit we have the following conventions - kernel is built with movq_cfi_restore 5*8+\offset, rbx .endm + .macro ZERO_EXTRA_REGS + xorl %r15d, %r15d + xorl %r14d, %r14d + xorl %r13d, %r13d + xorl %r12d, %r12d + xorl %ebp, %ebp + xorl %ebx, %ebx + .endm + .macro RESTORE_C_REGS_HELPER rstor_rax=1, rstor_rcx=1, rstor_r11=1, rstor_r8910=1, rstor_rdx=1 .if \rstor_r11 movq_cfi_restore 6*8, r11 diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index ca3347a9dab5..3563107b5060 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -171,10 +171,11 @@ do { \ static inline void elf_common_init(struct thread_struct *t, struct pt_regs *regs, const u16 ds) { - regs->ax = regs->bx = regs->cx = regs->dx = 0; - regs->si = regs->di = regs->bp = 0; + /* Commented-out registers are cleared in stub_execve */ + /*regs->ax = regs->bx =*/ regs->cx = regs->dx = 0; + regs->si = regs->di /*= regs->bp*/ = 0; regs->r8 = regs->r9 = regs->r10 = regs->r11 = 0; - regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0; + /*regs->r12 = regs->r13 = regs->r14 = regs->r15 = 0;*/ t->fs = t->gs = 0; t->fsindex = t->gsindex = 0; t->ds = t->es = ds; diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 386375d43d14..f4270ff73f2a 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -419,25 +419,27 @@ END(stub_\func) ENTRY(stub_execve) CFI_STARTPROC - addq $8, %rsp - DEFAULT_FRAME 0 - SAVE_EXTRA_REGS - call sys_execve - movq %rax,RAX(%rsp) - RESTORE_EXTRA_REGS - jmp int_ret_from_sys_call + DEFAULT_FRAME 0, 8 + call sys_execve +return_from_execve: + testl %eax, %eax + jz 1f + /* exec failed, can use fast SYSRET code path in this case */ + ret +1: + /* must use IRET code path (pt_regs->cs may have changed) */ + addq $8, %rsp + ZERO_EXTRA_REGS + movq %rax,RAX(%rsp) + jmp int_ret_from_sys_call CFI_ENDPROC END(stub_execve) ENTRY(stub_execveat) CFI_STARTPROC - addq $8, %rsp - DEFAULT_FRAME 0 - SAVE_EXTRA_REGS - call sys_execveat - movq %rax,RAX(%rsp) - RESTORE_EXTRA_REGS - jmp int_ret_from_sys_call + DEFAULT_FRAME 0, 8 + call sys_execveat + jmp return_from_execve CFI_ENDPROC END(stub_execveat) @@ -472,25 +474,17 @@ END(stub_x32_rt_sigreturn) ENTRY(stub_x32_execve) CFI_STARTPROC - addq $8, %rsp - DEFAULT_FRAME 0 - SAVE_EXTRA_REGS - call compat_sys_execve - movq %rax,RAX(%rsp) - RESTORE_EXTRA_REGS - jmp int_ret_from_sys_call + DEFAULT_FRAME 0, 8 + call compat_sys_execve + jmp return_from_execve CFI_ENDPROC END(stub_x32_execve) ENTRY(stub_x32_execveat) CFI_STARTPROC - addq $8, %rsp - DEFAULT_FRAME 0 - SAVE_EXTRA_REGS - call compat_sys_execveat - movq %rax,RAX(%rsp) - RESTORE_EXTRA_REGS - jmp int_ret_from_sys_call + DEFAULT_FRAME 0, 8 + call compat_sys_execveat + jmp return_from_execve CFI_ENDPROC END(stub_x32_execveat) -- 2.34.1