From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: [PATCH] x86/traps: Improve hypervisor stack overflow detection Date: Mon, 15 Feb 2016 10:03:16 +0000 Message-ID: <1455530596-14548-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Xen-devel Cc: Andrew Cooper , Jan Beulich List-Id: xen-devel@lists.xenproject.org A sample Gentoo compliation of Xen contains lea -0x1058(%rsp),%rsp orq $0x0,(%rsp) lea 0x1020(%rsp),%rsp Whatever the reason for silly code like this, it fools the current stack overflow detection logic in the #DF handler (which triggers reliably on the 'orq' instruction). Update the overflow condition to declare an overflow if %esp is anywhere within the guard page, rather than just within the upper 8th of the page. Additionally, check %esp against the expected stack base in all builds. Signed-off-by: Andrew Cooper --- CC: Jan Beulich v2: Reintroduce 512 bytes of slop on top of the guard page. --- xen/arch/x86/traps.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c index 26a5026..3604753 100644 --- a/xen/arch/x86/traps.c +++ b/xen/arch/x86/traps.c @@ -451,10 +451,17 @@ void show_stack(const struct cpu_user_regs *regs) void show_stack_overflow(unsigned int cpu, const struct cpu_user_regs *regs) { -#ifdef MEMORY_GUARD unsigned long esp = regs->rsp; + unsigned long curr_stack_base = esp & ~(STACK_SIZE - 1); +#ifdef MEMORY_GUARD unsigned long esp_top, esp_bottom; +#endif + + if ( _p(curr_stack_base) != stack_base[cpu] ) + printk("Current stack base %p differs from expected %p\n", + _p(curr_stack_base), stack_base[cpu]); +#ifdef MEMORY_GUARD esp_bottom = (esp | (STACK_SIZE - 1)) + 1; esp_top = esp_bottom - PRIMARY_STACK_SIZE; @@ -462,9 +469,12 @@ void show_stack_overflow(unsigned int cpu, const struct cpu_user_regs *regs) (void *)esp_top, (void *)esp_bottom, (void *)esp, (void *)per_cpu(init_tss, cpu).esp0); - /* Trigger overflow trace if %esp is within 512 bytes of the guard page. */ - if ( ((unsigned long)(esp - esp_top) > 512) && - ((unsigned long)(esp_top - esp) > 512) ) + /* + * Trigger overflow trace if %esp is anywhere within the guard page, or + * with fewer than 512 bytes remaining on the primary stack. + */ + if ( (esp > (esp_top + 512)) || + (esp < (esp_top - PAGE_SIZE)) ) { printk("No stack overflow detected. Skipping stack trace.\n"); return; -- 2.1.4