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SubjectRe: [PATCH] x86/asm/entry/32: Update ENOSYS handling to match 64-bit logic
On Fri, Apr 10, 2015 at 8:33 AM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
> Sometime ago Andy changed 64-bit syscall logic so that pt_regs->ax is
> initially set to -ENOSYS, and on exit from syscall, it is updated with
> actual return value. This simplified logic there.
>
> This patch does the same for 32-bit syscall entry points.
>
> The check for %rax being too big is moved to be just before
> the call insn which dispatches execution through syscall table.
> There is no way to accidentally skip this check now by jumping
> to a label after it. This allows to remove redundant checks
> after e.g. ptrace.
>
> If %rax is too big, we just skip over the (call, write %rax to pt_regs->ax)
> insn pair. pt_regs->ax remains set to -ENOSYS, and it gets returned
> to userspace.

This looks okay, but I'll read it again later today.

At the very least, though, this should be tested against the seccomp test suite.

--Andy

>
> Similar to 64-bit code, this eliminates "ia32_badsys" code path.
>
> Run-tested.
>
> Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
> CC: Linus Torvalds <torvalds@linux-foundation.org>
> CC: Steven Rostedt <rostedt@goodmis.org>
> CC: Ingo Molnar <mingo@kernel.org>
> CC: Borislav Petkov <bp@alien8.de>
> CC: "H. Peter Anvin" <hpa@zytor.com>
> CC: Andy Lutomirski <luto@amacapital.net>
> CC: Oleg Nesterov <oleg@redhat.com>
> CC: Frederic Weisbecker <fweisbec@gmail.com>
> CC: Alexei Starovoitov <ast@plumgrid.com>
> CC: Will Drewry <wad@chromium.org>
> CC: Kees Cook <keescook@chromium.org>
> CC: x86@kernel.org
> CC: linux-kernel@vger.kernel.org
> ---
> arch/x86/ia32/ia32entry.S | 44 +++++++++++++++-----------------------------
> 1 file changed, 15 insertions(+), 29 deletions(-)
>
> diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
> index a821b1c..29ab1c2 100644
> --- a/arch/x86/ia32/ia32entry.S
> +++ b/arch/x86/ia32/ia32entry.S
> @@ -142,7 +142,7 @@ ENTRY(ia32_sysenter_target)
> pushq_cfi_reg rsi /* pt_regs->si */
> pushq_cfi_reg rdx /* pt_regs->dx */
> pushq_cfi_reg rcx /* pt_regs->cx */
> - pushq_cfi_reg rax /* pt_regs->ax */
> + pushq_cfi $-ENOSYS /* pt_regs->ax */
> cld
> sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
> CFI_ADJUST_CFA_OFFSET 10*8
> @@ -169,8 +169,6 @@ sysenter_flags_fixed:
> testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
> CFI_REMEMBER_STATE
> jnz sysenter_tracesys
> - cmpq $(IA32_NR_syscalls-1),%rax
> - ja ia32_badsys
> sysenter_do_call:
> /* 32bit syscall -> 64bit C ABI argument conversion */
> movl %edi,%r8d /* arg5 */
> @@ -179,8 +177,11 @@ sysenter_do_call:
> movl %ebx,%edi /* arg1 */
> movl %edx,%edx /* arg3 (zero extension) */
> sysenter_dispatch:
> + cmpq $(IA32_NR_syscalls-1),%rax
> + ja 1f
> call *ia32_sys_call_table(,%rax,8)
> movq %rax,RAX(%rsp)
> +1:
> DISABLE_INTERRUPTS(CLBR_NONE)
> TRACE_IRQS_OFF
> testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
> @@ -247,9 +248,7 @@ sysexit_from_sys_call:
> movl %ebx,%esi /* 2nd arg: 1st syscall arg */
> movl %eax,%edi /* 1st arg: syscall number */
> call __audit_syscall_entry
> - movl RAX(%rsp),%eax /* reload syscall number */
> - cmpq $(IA32_NR_syscalls-1),%rax
> - ja ia32_badsys
> + movl ORIG_RAX(%rsp),%eax /* reload syscall number */
> movl %ebx,%edi /* reload 1st syscall arg */
> movl RCX(%rsp),%esi /* reload 2nd syscall arg */
> movl RDX(%rsp),%edx /* reload 3rd syscall arg */
> @@ -269,7 +268,7 @@ sysexit_from_sys_call:
> 1: setbe %al /* 1 if error, 0 if not */
> movzbl %al,%edi /* zero-extend that into %edi */
> call __audit_syscall_exit
> - movq RAX(%rsp),%rax /* reload syscall return value */
> + movq ORIG_RAX(%rsp),%rax /* reload syscall return value */
> movl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),%edi
> DISABLE_INTERRUPTS(CLBR_NONE)
> TRACE_IRQS_OFF
> @@ -300,13 +299,10 @@ sysenter_tracesys:
> #endif
> SAVE_EXTRA_REGS
> CLEAR_RREGS
> - movq $-ENOSYS,RAX(%rsp)/* ptrace can change this for a bad syscall */
> movq %rsp,%rdi /* &pt_regs -> arg1 */
> call syscall_trace_enter
> LOAD_ARGS32 /* reload args from stack in case ptrace changed it */
> RESTORE_EXTRA_REGS
> - cmpq $(IA32_NR_syscalls-1),%rax
> - ja int_ret_from_sys_call /* sysenter_tracesys has set RAX(%rsp) */
> jmp sysenter_do_call
> CFI_ENDPROC
> ENDPROC(ia32_sysenter_target)
> @@ -376,7 +372,7 @@ ENTRY(ia32_cstar_target)
> pushq_cfi_reg rdx /* pt_regs->dx */
> pushq_cfi_reg rbp /* pt_regs->cx */
> movl %ebp,%ecx
> - pushq_cfi_reg rax /* pt_regs->ax */
> + pushq_cfi $-ENOSYS /* pt_regs->ax */
> sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
> CFI_ADJUST_CFA_OFFSET 10*8
>
> @@ -392,8 +388,6 @@ ENTRY(ia32_cstar_target)
> testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
> CFI_REMEMBER_STATE
> jnz cstar_tracesys
> - cmpq $IA32_NR_syscalls-1,%rax
> - ja ia32_badsys
> cstar_do_call:
> /* 32bit syscall -> 64bit C ABI argument conversion */
> movl %edi,%r8d /* arg5 */
> @@ -402,8 +396,11 @@ cstar_do_call:
> movl %ebx,%edi /* arg1 */
> movl %edx,%edx /* arg3 (zero extension) */
> cstar_dispatch:
> + cmpq $(IA32_NR_syscalls-1),%rax
> + ja 1f
> call *ia32_sys_call_table(,%rax,8)
> movq %rax,RAX(%rsp)
> +1:
> DISABLE_INTERRUPTS(CLBR_NONE)
> TRACE_IRQS_OFF
> testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
> @@ -450,14 +447,11 @@ cstar_tracesys:
> xchgl %r9d,%ebp
> SAVE_EXTRA_REGS
> CLEAR_RREGS r9
> - movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
> movq %rsp,%rdi /* &pt_regs -> arg1 */
> call syscall_trace_enter
> LOAD_ARGS32 1 /* reload args from stack in case ptrace changed it */
> RESTORE_EXTRA_REGS
> xchgl %ebp,%r9d
> - cmpq $(IA32_NR_syscalls-1),%rax
> - ja int_ret_from_sys_call /* cstar_tracesys has set RAX(%rsp) */
> jmp cstar_do_call
> END(ia32_cstar_target)
>
> @@ -516,7 +510,7 @@ ENTRY(ia32_syscall)
> pushq_cfi_reg rsi /* pt_regs->si */
> pushq_cfi_reg rdx /* pt_regs->dx */
> pushq_cfi_reg rcx /* pt_regs->cx */
> - pushq_cfi_reg rax /* pt_regs->ax */
> + pushq_cfi $-ENOSYS /* pt_regs->ax */
> cld
> sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
> CFI_ADJUST_CFA_OFFSET 10*8
> @@ -524,8 +518,6 @@ ENTRY(ia32_syscall)
> orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
> testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
> jnz ia32_tracesys
> - cmpq $(IA32_NR_syscalls-1),%rax
> - ja ia32_badsys
> ia32_do_call:
> /* 32bit syscall -> 64bit C ABI argument conversion */
> movl %edi,%r8d /* arg5 */
> @@ -533,9 +525,12 @@ ia32_do_call:
> xchg %ecx,%esi /* rsi:arg2, rcx:arg4 */
> movl %ebx,%edi /* arg1 */
> movl %edx,%edx /* arg3 (zero extension) */
> + cmpq $(IA32_NR_syscalls-1),%rax
> + ja 1f
> call *ia32_sys_call_table(,%rax,8) # xxx: rip relative
> ia32_sysret:
> movq %rax,RAX(%rsp)
> +1:
> ia32_ret_from_sys_call:
> CLEAR_RREGS
> jmp int_ret_from_sys_call
> @@ -543,23 +538,14 @@ ia32_ret_from_sys_call:
> ia32_tracesys:
> SAVE_EXTRA_REGS
> CLEAR_RREGS
> - movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
> movq %rsp,%rdi /* &pt_regs -> arg1 */
> call syscall_trace_enter
> LOAD_ARGS32 /* reload args from stack in case ptrace changed it */
> RESTORE_EXTRA_REGS
> - cmpq $(IA32_NR_syscalls-1),%rax
> - ja int_ret_from_sys_call /* ia32_tracesys has set RAX(%rsp) */
> jmp ia32_do_call
> + CFI_ENDPROC
> END(ia32_syscall)
>
> -ia32_badsys:
> - movq $0,ORIG_RAX(%rsp)
> - movq $-ENOSYS,%rax
> - jmp ia32_sysret
> -
> - CFI_ENDPROC
> -
> .macro PTREGSCALL label, func
> ALIGN
> GLOBAL(\label)
> --
> 1.8.1.4
>



--
Andy Lutomirski
AMA Capital Management, LLC


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