From: "Jan Beulich" <JBeulich@suse.com>
To: "xen-devel" <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>, WeiLiu <wl@xen.org>,
Roger Pau Monne <roger.pau@citrix.com>
Subject: [Xen-devel] [PATCH v2 1/2] x86/traps: guard top-of-stack reads
Date: Mon, 17 Jun 2019 02:12:47 -0600 [thread overview]
Message-ID: <5D074B7F0200007800238B69@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <5D074AE60200007800238B5E@prv1-mh.provo.novell.com>
Nothing (afaics) guarantees that the original frame's stack pointer
points at readable memory. Avoid a (likely nested) crash by attaching
exception recovery to the read (making it a single read at the same
time). Don't even invoke _show_trace() in case of a non-readable top
slot.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v2: Name asm() arguments. Use explicit "fault" variable.
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -484,17 +484,31 @@ static void _show_trace(unsigned long sp
static void show_trace(const struct cpu_user_regs *regs)
{
- unsigned long *sp = ESP_BEFORE_EXCEPTION(regs);
+ unsigned long *sp = ESP_BEFORE_EXCEPTION(regs), tos = 0;
+ bool fault = false;
printk("Xen call trace:\n");
+ /* Guarded read of the stack top. */
+ asm ( "1: mov %[data], %[tos]; 2:\n"
+ ".pushsection .fixup,\"ax\"\n"
+ "3: movb $1, %[fault]; jmp 2b\n"
+ ".popsection\n"
+ _ASM_EXTABLE(1b, 3b)
+ : [tos] "+r" (tos), [fault] "+qm" (fault) : [data] "m" (*sp) );
+
/*
* If RIP looks sensible, or the top of the stack doesn't, print RIP at
* the top of the stack trace.
*/
if ( is_active_kernel_text(regs->rip) ||
- !is_active_kernel_text(*sp) )
+ !is_active_kernel_text(tos) )
printk(" [<%p>] %pS\n", _p(regs->rip), _p(regs->rip));
+ else if ( fault )
+ {
+ printk(" [Fault on access]\n");
+ return;
+ }
/*
* Else RIP looks bad but the top of the stack looks good. Perhaps we
* followed a wild function pointer? Lets assume the top of the stack is a
@@ -503,7 +517,7 @@ static void show_trace(const struct cpu_
*/
else
{
- printk(" [<%p>] %pS\n", _p(*sp), _p(*sp));
+ printk(" [<%p>] %pS\n", _p(tos), _p(tos));
sp++;
}
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next prev parent reply other threads:[~2019-06-17 8:13 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-31 8:59 [PATCH 0/2]: x86/traps: improve show_trace()'s top-of-stack handling Jan Beulich
2019-05-31 8:59 ` [Xen-devel] " Jan Beulich
2019-05-31 9:17 ` [PATCH 1/2] x86/traps: guard top-of-stack reads Jan Beulich
2019-05-31 9:17 ` [Xen-devel] " Jan Beulich
2019-06-07 17:51 ` Andrew Cooper
2019-06-11 9:57 ` Jan Beulich
2019-05-31 9:22 ` [PATCH 2/2] x86/traps: widen condition for logging top-of-stack Jan Beulich
2019-05-31 9:22 ` [Xen-devel] " Jan Beulich
2019-06-07 18:01 ` Andrew Cooper
2019-06-11 9:46 ` Jan Beulich
2019-06-17 8:10 ` [Xen-devel] [PATCH v2 0/2]: x86/traps: improve show_trace()'s top-of-stack handling Jan Beulich
2019-06-17 8:12 ` Jan Beulich [this message]
2019-07-02 17:47 ` [Xen-devel] [PATCH v2 1/2] x86/traps: guard top-of-stack reads Andrew Cooper
2019-07-03 7:10 ` Jan Beulich
2019-06-17 8:13 ` [Xen-devel] [PATCH v2 2/2] x86/traps: widen condition for logging top-of-stack Jan Beulich
2019-07-03 10:21 ` Andrew Cooper
2019-07-03 10:34 ` Jan Beulich
2019-07-03 19:47 ` Andrew Cooper
2019-07-04 9:09 ` Jan Beulich
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