From: Joe Lawrence <joe.lawrence@redhat.com>
To: linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
live-patching@vger.kernel.org
Cc: Nicolai Stange <nstange@suse.de>, Jiri Kosina <jkosina@suse.cz>,
Josh Poimboeuf <jpoimboe@redhat.com>, Torsten Duwe <duwe@lst.de>
Subject: [PATCH 2/4] powerpc/livepatch: relax reliable stack tracer checks for first-frame
Date: Tue, 22 Jan 2019 10:57:22 -0500 [thread overview]
Message-ID: <20190122155724.27557-3-joe.lawrence@redhat.com> (raw)
In-Reply-To: <20190122155724.27557-1-joe.lawrence@redhat.com>
The bottom-most stack frame (the first to be unwound) may be largely
uninitialized, for the "Power Architecture 64-Bit ELF V2 ABI" only
requires its backchain pointer to be set.
The reliable stack tracer should be careful when verifying this frame:
skip checks on STACK_FRAME_LR_SAVE and STACK_FRAME_MARKER offsets that
may contain uninitialized residual data.
Fixes: df78d3f61480 ("powerpc/livepatch: Implement reliable stack tracing for the consistency model")
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
arch/powerpc/kernel/stacktrace.c | 32 ++++++++++++++++++++++++--------
1 file changed, 24 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index e2c50b55138f..06688f4d557b 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -84,6 +84,12 @@ save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
EXPORT_SYMBOL_GPL(save_stack_trace_regs);
#ifdef CONFIG_HAVE_RELIABLE_STACKTRACE
+/*
+ * This function returns an error if it detects any unreliable features of the
+ * stack. Otherwise it guarantees that the stack trace is reliable.
+ *
+ * If the task is not 'current', the caller *must* ensure the task is inactive.
+ */
int
save_stack_trace_tsk_reliable(struct task_struct *tsk,
struct stack_trace *trace)
@@ -142,12 +148,6 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
if (sp & 0xF)
return 1;
- /* Mark stacktraces with exception frames as unreliable. */
- if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
- stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
- return 1;
- }
-
newsp = stack[0];
/* Stack grows downwards; unwinder may only go up. */
if (newsp <= sp)
@@ -158,11 +158,26 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
return 1; /* invalid backlink, too far up. */
}
+ /*
+ * We can only trust the bottom frame's backlink, the
+ * rest of the frame may be uninitialized, continue to
+ * the next.
+ */
+ if (firstframe) {
+ firstframe = 0;
+ goto next;
+ }
+
+ /* Mark stacktraces with exception frames as unreliable. */
+ if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
+ stack[STACK_FRAME_MARKER] == STACK_FRAME_REGS_MARKER) {
+ return 1;
+ }
+
/* Examine the saved LR: it must point into kernel code. */
ip = stack[STACK_FRAME_LR_SAVE];
- if (!firstframe && !__kernel_text_address(ip))
+ if (!__kernel_text_address(ip))
return 1;
- firstframe = 0;
/*
* FIXME: IMHO these tests do not belong in
@@ -183,6 +198,7 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
else
trace->skip--;
+next:
if (newsp == stack_end)
break;
--
2.20.1
next prev parent reply other threads:[~2019-01-22 16:03 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-22 15:57 [PATCH 0/4] powerpc/livepatch: reliable stack unwinder fixes Joe Lawrence
2019-01-22 15:57 ` [PATCH 1/4] powerpc/64s: Clear on-stack exception marker upon exception return Joe Lawrence
2019-01-30 12:27 ` Michael Ellerman
2019-01-30 17:18 ` Nicolai Stange
2019-01-31 5:46 ` Michael Ellerman
2019-02-02 1:14 ` Balbir Singh
2019-02-02 3:42 ` Balbir Singh
2019-02-05 11:24 ` Michael Ellerman
2019-02-06 2:48 ` Balbir Singh
2019-02-06 4:44 ` Michael Ellerman
2019-02-06 8:45 ` Balbir Singh
2019-02-08 13:02 ` [1/4] " Michael Ellerman
2019-01-22 15:57 ` Joe Lawrence [this message]
2019-01-22 15:57 ` [PATCH 3/4] powerpc/livepatch: small cleanups in save_stack_trace_tsk_reliable() Joe Lawrence
2019-01-22 15:57 ` [PATCH 4/4] powerpc/livepatch: return -ERRNO values " Joe Lawrence
2019-02-02 0:59 ` Balbir Singh
2019-01-29 21:10 ` [PATCH 0/4] powerpc/livepatch: reliable stack unwinder fixes Josh Poimboeuf
2019-01-29 23:50 ` Jiri Kosina
2019-01-30 12:22 ` Michael Ellerman
2019-01-30 13:28 ` Jiri Kosina
2019-01-31 5:46 ` Michael Ellerman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190122155724.27557-3-joe.lawrence@redhat.com \
--to=joe.lawrence@redhat.com \
--cc=duwe@lst.de \
--cc=jkosina@suse.cz \
--cc=jpoimboe@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=live-patching@vger.kernel.org \
--cc=nstange@suse.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).