From 6dc936f175cc6d12a8eb14d29b87e9238e460383 Mon Sep 17 00:00:00 2001 From: Dominik Brodowski Date: Thu, 5 Apr 2018 11:53:06 +0200 Subject: [PATCH] syscalls/x86: Extend register clearing on syscall entry to lower registers To reduce the chance that random user space content leaks down the call chain in registers, also clear lower registers on syscall entry: For 64-bit syscalls, extend the register clearing in PUSH_AND_CLEAR_REGS to %dx and %cx. This should not hurt at all, also on the other callers of that macro. We do not need to clear %rdi and %rsi for syscall entry, as those registers are used to pass the parameters to do_syscall_64(). For the 32-bit compat syscalls, do_int80_syscall_32() and do_fast_syscall_32() each only take one parameter. Therefore, extend the register clearing to %dx, %cx, and %si in entry_SYSCALL_compat and entry_INT80_compat. Signed-off-by: Dominik Brodowski Acked-by: Linus Torvalds Cc: Al Viro Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20180405095307.3730-8-linux@dominikbrodowski.net Signed-off-by: Ingo Molnar --- arch/x86/entry/calling.h | 2 ++ arch/x86/entry/entry_64_compat.S | 6 ++++++ 2 files changed, 8 insertions(+) diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h index be63330..352e70c 100644 --- a/arch/x86/entry/calling.h +++ b/arch/x86/entry/calling.h @@ -114,7 +114,9 @@ For 32-bit we have the following conventions - kernel is built with pushq %rsi /* pt_regs->si */ .endif pushq \rdx /* pt_regs->dx */ + xorl %edx, %edx /* nospec dx */ pushq %rcx /* pt_regs->cx */ + xorl %ecx, %ecx /* nospec cx */ pushq \rax /* pt_regs->ax */ pushq %r8 /* pt_regs->r8 */ xorl %r8d, %r8d /* nospec r8 */ diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S index 08425c4..9af927e 100644 --- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -220,8 +220,11 @@ GLOBAL(entry_SYSCALL_compat_after_hwframe) pushq %rax /* pt_regs->orig_ax */ pushq %rdi /* pt_regs->di */ pushq %rsi /* pt_regs->si */ + xorl %esi, %esi /* nospec si */ pushq %rdx /* pt_regs->dx */ + xorl %edx, %edx /* nospec dx */ pushq %rbp /* pt_regs->cx (stashed in bp) */ + xorl %ecx, %ecx /* nospec cx */ pushq $-ENOSYS /* pt_regs->ax */ pushq $0 /* pt_regs->r8 = 0 */ xorl %r8d, %r8d /* nospec r8 */ @@ -365,8 +368,11 @@ ENTRY(entry_INT80_compat) pushq (%rdi) /* pt_regs->di */ pushq %rsi /* pt_regs->si */ + xorl %esi, %esi /* nospec si */ pushq %rdx /* pt_regs->dx */ + xorl %edx, %edx /* nospec dx */ pushq %rcx /* pt_regs->cx */ + xorl %ecx, %ecx /* nospec cx */ pushq $-ENOSYS /* pt_regs->ax */ pushq $0 /* pt_regs->r8 = 0 */ xorl %r8d, %r8d /* nospec r8 */ -- 2.7.4