This is a note to let you know that I've just added the patch titled
x86/nospec: Fix i386 RSB stuffing
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-nospec-fix-i386-rsb-stuffing.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Tue Dec 6 01:29:51 PM CET 2022
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon, 5 Dec 2022 23:10:26 +0100
Subject: x86/nospec: Fix i386 RSB stuffing
To: stable@xxxxxxxxxxxxxxx
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Message-ID: <Y45sUiyu2/cjze66@xxxxxxxxxxxxxxx>
Content-Disposition: inline
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
commit 332924973725e8cdcc783c175f68cf7e162cb9e5 upstream.
Turns out that i386 doesn't unconditionally have LFENCE, as such the
loop in __FILL_RETURN_BUFFER isn't actually speculation safe on such
chips.
Fixes: ba6e31af2be9 ("x86/speculation: Add LFENCE to RSB fill sequence")
Reported-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/Yv9tj9vbQ9nNlXoY@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
[bwh: Backported to 4.14:
- __FILL_RETURN_BUFFER takes an sp parameter
- Open-code __FILL_RETURN_SLOT]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/include/asm/nospec-branch.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -38,6 +38,7 @@
* the optimal version — two calls, each with their own speculation
* trap should their return address end up getting used, in a loop.
*/
+#ifdef CONFIG_X86_64
#define __FILL_RETURN_BUFFER(reg, nr, sp) \
mov $(nr/2), reg; \
771: \
@@ -58,6 +59,19 @@
jnz 771b; \
/* barrier for jnz misprediction */ \
lfence;
+#else
+/*
+ * i386 doesn't unconditionally have LFENCE, as such it can't
+ * do a loop.
+ */
+#define __FILL_RETURN_BUFFER(reg, nr, sp) \
+ .rept nr; \
+ call 772f; \
+ int3; \
+772:; \
+ .endr; \
+ add $(BITS_PER_LONG/8) * nr, sp;
+#endif
#define ISSUE_UNBALANCED_RET_GUARD(sp) \
call 992f; \
Patches currently in stable-queue which might be from peterz@xxxxxxxxxxxxx are
queue-4.14/perf-add-sample_flags-to-indicate-the-pmu-filled-sam.patch
queue-4.14/x86-nospec-fix-i386-rsb-stuffing.patch
queue-4.14/revert-x86-speculation-change-fill_return_buffer-to-work-with-objtool.patch
