FAILED: patch "[PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4" failed to apply to 6.1-stable tree

FAILED: patch "[PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4" failed to apply to 6.1-stable tree

[gregkh]

The patch below does not apply to the 6.1-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-6.1.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 '2024033030-steam-implosion-5c12@gregkh' --subject-prefix 'PATCH 6.1.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 6.1-stable tree

[Borislav Petkov]

On Sat, Mar 30, 2024 at 10:46:30AM +0100, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.1-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>.

6.1 is easier, actually. 2 patches as a reply to this message.

Thx.

-- 
Regards/Gruss,
    Boris.

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

[PATCH 1/2] x86/bugs: Fix the SRSO mitigation on Zen3/4

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Thu, 28 Mar 2024 13:59:05 +0100

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  | 20 ++++++++++++++------
 arch/x86/lib/retpoline.S              |  4 +---
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
index 8f80de627c60..5cdccea45554 100644
--- a/arch/x86/include/asm/asm-prototypes.h
+++ b/arch/x86/include/asm/asm-prototypes.h
@@ -12,6 +12,7 @@
 #include <asm/special_insns.h>
 #include <asm/preempt.h>
 #include <asm/asm.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 8f6f17a8617b..47e4e06a47d7 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -167,11 +167,20 @@
 .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
 #ifdef CONFIG_CPU_UNRET_ENTRY
-#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
@@ -188,9 +197,8 @@
 #if defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_IBPB_ENTRY) || \
 	defined(CONFIG_CPU_SRSO)
 	ANNOTATE_UNRET_END
-	ALTERNATIVE_2 "",						\
-		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\
-		      "call entry_ibpb", X86_FEATURE_ENTRY_IBPB
+	CALL_UNTRAIN_RET
+	ALTERNATIVE "", "call entry_ibpb", X86_FEATURE_ENTRY_IBPB
 #endif
 .endm
 
diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 65c5c44f006b..24c850e1e239 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -252,9 +252,7 @@ SYM_CODE_START(srso_return_thunk)
 SYM_CODE_END(srso_return_thunk)
 
 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 2/2] x86/retpoline: Do the necessary fixup to the Zen3/4 srso return thunk for !SRSO

[Borislav Petkov]

From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Tue, 2 Apr 2024 16:05:49 +0200

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 | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S
index 24c850e1e239..a96e816e5ccd 100644
--- a/arch/x86/lib/retpoline.S
+++ b/arch/x86/lib/retpoline.S
@@ -110,6 +110,7 @@ SYM_START(srso_alias_untrain_ret, SYM_L_GLOBAL, SYM_A_NONE)
 	ret
 	int3
 SYM_FUNC_END(srso_alias_untrain_ret)
+__EXPORT_THUNK(srso_alias_untrain_ret)
 #endif
 
 SYM_START(srso_alias_safe_ret, SYM_L_GLOBAL, SYM_A_NONE)
-- 
2.43.0


-- 
Regards/Gruss,
    Boris.

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

Re: FAILED: patch "[PATCH] x86/bugs: Fix the SRSO mitigation on Zen3/4" failed to apply to 6.1-stable tree

[Greg KH]

On Fri, Apr 05, 2024 at 12:09:30PM +0200, Borislav Petkov wrote:
> On Sat, Mar 30, 2024 at 10:46:30AM +0100, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 6.1-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>.
> 
> 6.1 is easier, actually. 2 patches as a reply to this message.

Both now queued up, thanks.

greg k-h