FAILED: patch "[PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4" failed to apply to 6.8-stable tree

FAILED: patch "[PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4" failed to apply to 6.8-stable tree

[gregkh]

The patch below does not apply to the 6.8-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 <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.8.y
git checkout FETCH_HEAD
git cherry-pick -x 4535e1a4174c4111d92c5a9a21e542d232e0fcaa
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024033027-tapered-curly-3516@gregkh' --subject-prefix 'PATCH 6.8.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 4535e1a4174c4111d92c5a9a21e542d232e0fcaa Mon Sep 17 00:00:00 2001
From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Thu, 28 Mar 2024 13:59:05 +0100
Subject: [PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4

The original version of the mitigation would patch in the calls to the
untraining routines directly.  That is, the alternative() in UNTRAIN_RET
will patch in the CALL to srso_alias_untrain_ret() directly.

However, even if commit e7c25c441e9e ("x86/cpu: Cleanup the untrain
mess") meant well in trying to clean up the situation, due to micro-
architectural reasons, the untraining routine srso_alias_untrain_ret()
must be the target of a CALL instruction and not of a JMP instruction as
it is done now.

Reshuffle the alternative macros to accomplish that.

Fixes: e7c25c441e9e ("x86/cpu: Cleanup the untrain mess")
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index 076bf8dee702..25466c4d2134 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -14,6 +14,7 @@
 #include <asm/asm.h>
 #include <asm/fred.h>
 #include <asm/gsseg.h>
+#include <asm/nospec-branch.h>
 
 #ifndef CONFIG_X86_CMPXCHG64
 extern void cmpxchg8b_emu(void);
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index fc3a8a3c7ffe..170c89ed22fc 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -262,11 +262,20 @@
 .Lskip_rsb_\@:
 .endm
 
+/*
+ * The CALL to srso_alias_untrain_ret() must be patched in directly at
+ * the spot where untraining must be done, ie., srso_alias_untrain_ret()
+ * must be the target of a CALL instruction instead of indirectly
+ * jumping to a wrapper which then calls it. Therefore, this macro is
+ * called outside of __UNTRAIN_RET below, for the time being, before the
+ * kernel can support nested alternatives with arbitrary nesting.
+ */
+.macro CALL_UNTRAIN_RET
 #if defined(CONFIG_MITIGATION_UNRET_ENTRY) || defined(CONFIG_MITIGATION_SRSO)
-#define CALL_UNTRAIN_RET	"call entry_untrain_ret"
-#else
-#define CALL_UNTRAIN_RET	""
+	ALTERNATIVE_2 "", "call entry_untrain_ret", X86_FEATURE_UNRET, \
+		          "call srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS
 #endif
+.endm
 
 /*
  * Mitigate RETBleed for AMD/Hygon Zen uarch. Requires KERNEL CR3 because the
@@ -282,8 +291,8 @@
 .macro __UNTRAIN_RET ibpb_feature, call_depth_insns
 #if defined(CONFIG_MITIGATION_RETHUNK) || defined(CONFIG_MITIGATION_IBPB_ENTRY)
 	VALIDATE_UNRET_END
-	ALTERNATIVE_3 "",						\
-		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\
+	CALL_UNTRAIN_RET
+	ALTERNATIVE_2 "",						\
 		      "call entry_ibpb", \ibpb_feature,			\
 		     __stringify(\call_depth_insns), X86_FEATURE_CALL_DEPTH
 #endif
@@ -342,6 +351,8 @@ extern void retbleed_return_thunk(void);
 static inline void retbleed_return_thunk(void) {}
 #endif
 
+extern void srso_alias_untrain_ret(void);
+
 #ifdef CONFIG_MITIGATION_SRSO
 extern void srso_return_thunk(void);
 extern void srso_alias_return_thunk(void);
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 721b528da9ac..02cde194a99e 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -163,6 +163,7 @@ SYM_CODE_START_NOALIGN(srso_alias_untrain_ret)
 	lfence
 	jmp srso_alias_return_thunk
 SYM_FUNC_END(srso_alias_untrain_ret)
+__EXPORT_THUNK(srso_alias_untrain_ret)
 	.popsection
 
 	.pushsection .text..__x86.rethunk_safe
@@ -224,10 +225,12 @@ SYM_CODE_START(srso_return_thunk)
 SYM_CODE_END(srso_return_thunk)
 
 #define JMP_SRSO_UNTRAIN_RET "jmp srso_untrain_ret"
-#define JMP_SRSO_ALIAS_UNTRAIN_RET "jmp srso_alias_untrain_ret"
 #else /* !CONFIG_MITIGATION_SRSO */
+/* Dummy for the alternative in CALL_UNTRAIN_RET. */
+SYM_CODE_START(srso_alias_untrain_ret)
+	RET
+SYM_FUNC_END(srso_alias_untrain_ret)
 #define JMP_SRSO_UNTRAIN_RET "ud2"
-#define JMP_SRSO_ALIAS_UNTRAIN_RET "ud2"
 #endif /* CONFIG_MITIGATION_SRSO */
 
 #ifdef CONFIG_MITIGATION_UNRET_ENTRY
@@ -319,9 +322,7 @@ SYM_FUNC_END(retbleed_untrain_ret)
 #if defined(CONFIG_MITIGATION_UNRET_ENTRY) || defined(CONFIG_MITIGATION_SRSO)
 
 SYM_FUNC_START(entry_untrain_ret)
-	ALTERNATIVE_2 JMP_RETBLEED_UNTRAIN_RET,				\
-		      JMP_SRSO_UNTRAIN_RET, X86_FEATURE_SRSO,		\
-		      JMP_SRSO_ALIAS_UNTRAIN_RET, X86_FEATURE_SRSO_ALIAS
+	ALTERNATIVE JMP_RETBLEED_UNTRAIN_RET, JMP_SRSO_UNTRAIN_RET, X86_FEATURE_SRSO
 SYM_FUNC_END(entry_untrain_ret)
 __EXPORT_THUNK(entry_untrain_ret)
 

Re: FAILED: patch "[PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4" failed to apply to 6.8-stable tree

[Borislav Petkov]

On Sat, Mar 30, 2024 at 10:46:27AM +0100, gregkh@linuxfoundation.org wrote:
> The patch below does not apply to the 6.8-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 <stable@vger.kernel.org>.

Here it is:

---
From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Thu, 28 Mar 2024 13:59:05 +0100
Subject: [PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4

Commit 4535e1a4174c4111d92c5a9a21e542d232e0fcaa upstream.

The original version of the mitigation would patch in the calls to the
untraining routines directly.  That is, the alternative() in UNTRAIN_RET
will patch in the CALL to srso_alias_untrain_ret() directly.

However, even if commit e7c25c441e9e ("x86/cpu: Cleanup the untrain
mess") meant well in trying to clean up the situation, due to micro-
architectural reasons, the untraining routine srso_alias_untrain_ret()
must be the target of a CALL instruction and not of a JMP instruction as
it is done now.

Reshuffle the alternative macros to accomplish that.

Fixes: e7c25c441e9e ("x86/cpu: Cleanup the untrain mess")
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 arch/x86/include/asm/asm-prototypes.h |  1 +
 arch/x86/include/asm/nospec-branch.h  | 21 ++++++++++++++++-----
 arch/x86/lib/retpoline.S              | 11 ++++++-----
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index b1a98fa38828..0e82074517f6 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -13,6 +13,7 @@
 #include <asm/preempt.h>
 #include <asm/asm.h>
 #include <asm/gsseg.h>
+#include <asm/nospec-branch.h>
 
 #ifndef CONFIG_X86_CMPXCHG64
 extern void cmpxchg8b_emu(void);
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 2aa52cab1e46..93c3e28dd8e0 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -271,11 +271,20 @@
 .Lskip_rsb_\@:
 .endm
 
+/*
+ * The CALL to srso_alias_untrain_ret() must be patched in directly at
+ * the spot where untraining must be done, ie., srso_alias_untrain_ret()
+ * must be the target of a CALL instruction instead of indirectly
+ * jumping to a wrapper which then calls it. Therefore, this macro is
+ * called outside of __UNTRAIN_RET below, for the time being, before the
+ * kernel can support nested alternatives with arbitrary nesting.
+ */
+.macro CALL_UNTRAIN_RET
 #if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_SRSO)
-#define CALL_UNTRAIN_RET	"call entry_untrain_ret"
-#else
-#define CALL_UNTRAIN_RET	""
+	ALTERNATIVE_2 "", "call entry_untrain_ret", X86_FEATURE_UNRET, \
+		          "call srso_alias_untrain_ret", X86_FEATURE_SRSO_ALIAS
 #endif
+.endm
 
 /*
  * Mitigate RETBleed for AMD/Hygon Zen uarch. Requires KERNEL CR3 because the
@@ -291,8 +300,8 @@
 .macro __UNTRAIN_RET ibpb_feature, call_depth_insns
 #if defined(CONFIG_RETHUNK) || defined(CONFIG_CPU_IBPB_ENTRY)
 	VALIDATE_UNRET_END
-	ALTERNATIVE_3 "",						\
-		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\
+	CALL_UNTRAIN_RET
+	ALTERNATIVE_2 "",						\
 		      "call entry_ibpb", \ibpb_feature,			\
 		     __stringify(\call_depth_insns), X86_FEATURE_CALL_DEPTH
 #endif
@@ -351,6 +360,8 @@ extern void retbleed_return_thunk(void);
 static inline void retbleed_return_thunk(void) {}
 #endif
 
+extern void srso_alias_untrain_ret(void);
+
 #ifdef CONFIG_CPU_SRSO
 extern void srso_return_thunk(void);
 extern void srso_alias_return_thunk(void);
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 7b2589877d06..1e59367b4681 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -163,6 +163,7 @@ SYM_CODE_START_NOALIGN(srso_alias_untrain_ret)
 	lfence
 	jmp srso_alias_return_thunk
 SYM_FUNC_END(srso_alias_untrain_ret)
+__EXPORT_THUNK(srso_alias_untrain_ret)
 	.popsection
 
 	.pushsection .text..__x86.rethunk_safe
@@ -224,10 +225,12 @@ SYM_CODE_START(srso_return_thunk)
 SYM_CODE_END(srso_return_thunk)
 
 #define JMP_SRSO_UNTRAIN_RET "jmp srso_untrain_ret"
-#define JMP_SRSO_ALIAS_UNTRAIN_RET "jmp srso_alias_untrain_ret"
 #else /* !CONFIG_CPU_SRSO */
 #define JMP_SRSO_UNTRAIN_RET "ud2"
-#define JMP_SRSO_ALIAS_UNTRAIN_RET "ud2"
+/* Dummy for the alternative in CALL_UNTRAIN_RET. */
+SYM_CODE_START(srso_alias_untrain_ret)
+	RET
+SYM_FUNC_END(srso_alias_untrain_ret)
 #endif /* CONFIG_CPU_SRSO */
 
 #ifdef CONFIG_CPU_UNRET_ENTRY
@@ -319,9 +322,7 @@ SYM_FUNC_END(retbleed_untrain_ret)
 #if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_SRSO)
 
 SYM_FUNC_START(entry_untrain_ret)
-	ALTERNATIVE_2 JMP_RETBLEED_UNTRAIN_RET,				\
-		      JMP_SRSO_UNTRAIN_RET, X86_FEATURE_SRSO,		\
-		      JMP_SRSO_ALIAS_UNTRAIN_RET, X86_FEATURE_SRSO_ALIAS
+	ALTERNATIVE JMP_RETBLEED_UNTRAIN_RET, JMP_SRSO_UNTRAIN_RET, X86_FEATURE_SRSO
 SYM_FUNC_END(entry_untrain_ret)
 __EXPORT_THUNK(entry_untrain_ret)
 
-- 
2.43.0


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

[PATCH] x86/retpoline: Do the necessary fixup to the Zen3/4 srso return thunk for !SRSO (was: Re: FAILED: patch "[PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4" failed to apply to 6.8-stable tree)

[Borislav Petkov]

On Sat, Mar 30, 2024 at 11:40:26PM +0100, Borislav Petkov wrote:
> From: "Borislav Petkov (AMD)" <bp@alien8.de>
> Date: Thu, 28 Mar 2024 13:59:05 +0100
> Subject: [PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4
> 
> Commit 4535e1a4174c4111d92c5a9a21e542d232e0fcaa upstream.

One more ontop because one is clearly not enough and I'm a moron. :-\

From 20ff7c032fae1f6c78bc6bf06ea9a3f2bc3cb207 Mon Sep 17 00:00:00 2001
From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Tue, 2 Apr 2024 16:05:49 +0200
Subject: [PATCH] x86/retpoline: Do the necessary fixup to the Zen3/4 srso return thunk for !SRSO

Commit 0e110732473e14d6520e49d75d2c88ef7d46fe67 upstream.

The srso_alias_untrain_ret() dummy thunk in the !CONFIG_MITIGATION_SRSO
case is there only for the altenative in CALL_UNTRAIN_RET to have
a symbol to resolve.

However, testing with kernels which don't have CONFIG_MITIGATION_SRSO
enabled, leads to the warning in patch_return() to fire:

  missing return thunk: srso_alias_untrain_ret+0x0/0x10-0x0: eb 0e 66 66 2e
  WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:826 apply_returns (arch/x86/kernel/alternative.c:826

Put in a plain "ret" there so that gcc doesn't put a return thunk in
in its place which special and gets checked.

In addition:

  ERROR: modpost: "srso_alias_untrain_ret" [arch/x86/kvm/kvm-amd.ko] undefined!
  make[2]: *** [scripts/Makefile.modpost:145: Module.symvers] Chyba 1
  make[1]: *** [/usr/src/linux-6.8.3/Makefile:1873: modpost] Chyba 2
  make: *** [Makefile:240: __sub-make] Chyba 2

since !SRSO builds would use the dummy return thunk as reported by
petr.pisar@atlas.cz, https://bugzilla.kernel.org/show_bug.cgi?id=218679.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202404020901.da75a60f-oliver.sang@intel.com
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/all/202404020901.da75a60f-oliver.sang@intel.com/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 arch/x86/lib/retpoline.S | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 1e59367b4681..7c51a5323eca 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -229,8 +229,11 @@ SYM_CODE_END(srso_return_thunk)
 #define JMP_SRSO_UNTRAIN_RET "ud2"
 /* Dummy for the alternative in CALL_UNTRAIN_RET. */
 SYM_CODE_START(srso_alias_untrain_ret)
-	RET
+	ANNOTATE_UNRET_SAFE
+	ret
+	int3
 SYM_FUNC_END(srso_alias_untrain_ret)
+__EXPORT_THUNK(srso_alias_untrain_ret)
 #endif /* CONFIG_CPU_SRSO */
 
 #ifdef CONFIG_CPU_UNRET_ENTRY
-- 
2.43.0

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH] x86/retpoline: Do the necessary fixup to the Zen3/4 srso return thunk for !SRSO (was: Re: FAILED: patch "[PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4" failed to apply to 6.8-stable tree)

[Greg KH]

On Fri, Apr 05, 2024 at 11:36:51AM +0200, Borislav Petkov wrote:
> On Sat, Mar 30, 2024 at 11:40:26PM +0100, Borislav Petkov wrote:
> > From: "Borislav Petkov (AMD)" <bp@alien8.de>
> > Date: Thu, 28 Mar 2024 13:59:05 +0100
> > Subject: [PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4
> > 
> > Commit 4535e1a4174c4111d92c5a9a21e542d232e0fcaa upstream.
> 
> One more ontop because one is clearly not enough and I'm a moron. :-\

All now queued up, thanks.

greg k-h