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FAILED: patch "[PATCH] x86/nospec: Fix i386 RSB stuffing" failed to apply to 4.19-stable tree

PATCH [email protected] 1 participant 1 message Aug 29, 2022

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The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 332924973725e8cdcc783c175f68cf7e162cb9e5 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <[email protected]>
Date: Fri, 19 Aug 2022 13:01:35 +0200
Subject: [PATCH] x86/nospec: Fix i386 RSB stuffing

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 <[email protected]>
Signed-off-by Peter Zijlstra (Intel) <[email protected]>
Link https://lkml.kernel.org/r/[email protected] open here
arch/x86/include/asm/nospec-branch.h +12 -0
index 10731ccfed37..c936ce9f0c47 100644
@@ -50,6 +50,7 @@
  * 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)			\
 	mov	$(nr/2), reg;				\
 771:							\

@@ -60,6 +61,17 @@
 	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)			\
+	.rept nr;					\
+	__FILL_RETURN_SLOT;				\
+	.endr;						\
+	add	$(BITS_PER_LONG/8) * nr, %_ASM_SP;
+#endif
 
 /*
  * Stuff a single RSB slot.