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Date: Mon, 18 Sep 2017 11:11:40 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Borislav Petkov <bpetkov@...e.de>, Brian Gerst <brgerst@...il.com>, Chang Seok <chang.seok.bae@...el.com>, Denys Vlasenko <dvlasenk@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Josh Poimboeuf <jpoimboe@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org> Subject: [PATCH 4.12 46/52] x86/fsgsbase/64: Fully initialize FS and GS state in start_thread_common 4.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Andy Lutomirski <luto@...nel.org> commit 767d035d838f4fd6b5a5bbd7a3f6d293b7f65a49 upstream. execve used to leak FSBASE and GSBASE on AMD CPUs. Fix it. The security impact of this bug is small but not quite zero -- it could weaken ASLR when a privileged task execs a less privileged program, but only if program changed bitness across the exec, or the child binary was highly unusual or actively malicious. A child program that was compromised after the exec would not have access to the leaked base. Signed-off-by: Andy Lutomirski <luto@...nel.org> Cc: Borislav Petkov <bp@...en8.de> Cc: Borislav Petkov <bpetkov@...e.de> Cc: Brian Gerst <brgerst@...il.com> Cc: Chang Seok <chang.seok.bae@...el.com> Cc: Denys Vlasenko <dvlasenk@...hat.com> Cc: H. Peter Anvin <hpa@...or.com> Cc: Josh Poimboeuf <jpoimboe@...hat.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Thomas Gleixner <tglx@...utronix.de> Signed-off-by: Ingo Molnar <mingo@...nel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- arch/x86/kernel/process_64.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -229,10 +229,19 @@ start_thread_common(struct pt_regs *regs unsigned long new_sp, unsigned int _cs, unsigned int _ss, unsigned int _ds) { + WARN_ON_ONCE(regs != current_pt_regs()); + + if (static_cpu_has(X86_BUG_NULL_SEG)) { + /* Loading zero below won't clear the base. */ + loadsegment(fs, __USER_DS); + load_gs_index(__USER_DS); + } + loadsegment(fs, 0); loadsegment(es, _ds); loadsegment(ds, _ds); load_gs_index(0); + regs->ip = new_ip; regs->sp = new_sp; regs->cs = _cs;
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