[PATCH 6.1 0/3] ITS fixes

[PATCH 6.1 0/3] ITS fixes

[Pawan Gupta]

Two of the patches are older rethunk fixes and one is a build fix for
CONFIG_MODULES=n.

---
Borislav Petkov (AMD) (1):
      x86/alternative: Optimize returns patching

Eric Biggers (1):
      x86/its: Fix build errors when CONFIG_MODULES=n

Josh Poimboeuf (1):
      x86/alternatives: Remove faulty optimization

 arch/x86/kernel/alternative.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)
---
change-id: 20250513-its-fixes-6-1-d21ce20b0d1d

[PATCH 6.1 1/3] x86/alternative: Optimize returns patching

[Pawan Gupta]

From: "Borislav Petkov (AMD)" <bp@alien8.de>

commit d2408e043e7296017420aa5929b3bba4d5e61013 upstream.

Instead of decoding each instruction in the return sites range only to
realize that that return site is a jump to the default return thunk
which is needed - X86_FEATURE_RETHUNK is enabled - lift that check
before the loop and get rid of that loop overhead.

Add comments about what gets patched, while at it.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230512120952.7924-1-bp@alien8.de
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
 arch/x86/kernel/alternative.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 44bff34f7d10cb6868ad079ca1cb87e458d3f91b..dfd5490df0af9e55d1a6ab185ad7cb03bdda4a91 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -769,13 +769,12 @@ static int patch_return(void *addr, struct insn *insn, u8 *bytes)
 {
 	int i = 0;
 
+	/* Patch the custom return thunks... */
 	if (cpu_wants_rethunk_at(addr)) {
-		if (x86_return_thunk == __x86_return_thunk)
-			return -1;
-
 		i = JMP32_INSN_SIZE;
 		__text_gen_insn(bytes, JMP32_INSN_OPCODE, addr, x86_return_thunk, i);
 	} else {
+		/* ... or patch them out if not needed. */
 		bytes[i++] = RET_INSN_OPCODE;
 	}
 
@@ -788,6 +787,14 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end)
 {
 	s32 *s;
 
+	/*
+	 * Do not patch out the default return thunks if those needed are the
+	 * ones generated by the compiler.
+	 */
+	if (cpu_feature_enabled(X86_FEATURE_RETHUNK) &&
+	    (x86_return_thunk == __x86_return_thunk))
+		return;
+
 	for (s = start; s < end; s++) {
 		void *dest = NULL, *addr = (void *)s + *s;
 		struct insn insn;

-- 
2.34.1

[PATCH 6.1 2/3] x86/alternatives: Remove faulty optimization

[Pawan Gupta]

From: Josh Poimboeuf <jpoimboe@kernel.org>

commit 4ba89dd6ddeca2a733bdaed7c9a5cbe4e19d9124 upstream.

The following commit

  095b8303f383 ("x86/alternative: Make custom return thunk unconditional")

made '__x86_return_thunk' a placeholder value.  All code setting
X86_FEATURE_RETHUNK also changes the value of 'x86_return_thunk'.  So
the optimization at the beginning of apply_returns() is dead code.

Also, before the above-mentioned commit, the optimization actually had a
bug It bypassed __static_call_fixup(), causing some raw returns to
remain unpatched in static call trampolines.  Thus the 'Fixes' tag.

Fixes: d2408e043e72 ("x86/alternative: Optimize returns patching")
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/16d19d2249d4485d8380fb215ffaae81e6b8119e.1693889988.git.jpoimboe@kernel.org
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
 arch/x86/kernel/alternative.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index dfd5490df0af9e55d1a6ab185ad7cb03bdda4a91..023899e9ebd16ba223a1de91da9bcb43666788f9 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -787,14 +787,6 @@ void __init_or_module noinline apply_returns(s32 *start, s32 *end)
 {
 	s32 *s;
 
-	/*
-	 * Do not patch out the default return thunks if those needed are the
-	 * ones generated by the compiler.
-	 */
-	if (cpu_feature_enabled(X86_FEATURE_RETHUNK) &&
-	    (x86_return_thunk == __x86_return_thunk))
-		return;
-
 	for (s = start; s < end; s++) {
 		void *dest = NULL, *addr = (void *)s + *s;
 		struct insn insn;

-- 
2.34.1

[PATCH 6.1 3/3] x86/its: Fix build errors when CONFIG_MODULES=n

[Pawan Gupta]

From: Eric Biggers <ebiggers@google.com>

commit 9f35e33144ae5377d6a8de86dd3bd4d995c6ac65 upstream.

Fix several build errors when CONFIG_MODULES=n, including the following:

../arch/x86/kernel/alternative.c:195:25: error: incomplete definition of type 'struct module'
  195 |         for (int i = 0; i < mod->its_num_pages; i++) {

Fixes: 872df34d7c51 ("x86/its: Use dynamic thunks for indirect branches")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Dave Hansen <dave.hansen@intel.com>
Tested-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
 arch/x86/kernel/alternative.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 023899e9ebd16ba223a1de91da9bcb43666788f9..843bda0cb5d09a091a06ac7c3b30d5545880e905 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -402,7 +402,9 @@ static int emit_indirect(int op, int reg, u8 *bytes)
 
 #ifdef CONFIG_MITIGATION_ITS
 
+#ifdef CONFIG_MODULES
 static struct module *its_mod;
+#endif
 static void *its_page;
 static unsigned int its_offset;
 
@@ -423,6 +425,7 @@ static void *its_init_thunk(void *thunk, int reg)
 	return thunk;
 }
 
+#ifdef CONFIG_MODULES
 void its_init_mod(struct module *mod)
 {
 	if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS))
@@ -462,6 +465,7 @@ void its_free_mod(struct module *mod)
 	}
 	kfree(mod->its_page_array);
 }
+#endif /* CONFIG_MODULES */
 
 DEFINE_FREE(its_execmem, void *, if (_T) module_memfree(_T));
 
@@ -472,6 +476,7 @@ static void *its_alloc(void)
 	if (!page)
 		return NULL;
 
+#ifdef CONFIG_MODULES
 	if (its_mod) {
 		void *tmp = krealloc(its_mod->its_page_array,
 				     (its_mod->its_num_pages+1) * sizeof(void *),
@@ -482,6 +487,7 @@ static void *its_alloc(void)
 		its_mod->its_page_array = tmp;
 		its_mod->its_page_array[its_mod->its_num_pages++] = page;
 	}
+#endif /* CONFIG_MODULES */
 
 	return no_free_ptr(page);
 }

-- 
2.34.1

Re: [PATCH 6.1 1/3] x86/alternative: Optimize returns patching

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

Summary of potential issues:
⚠️ Found follow-up fixes in mainline

The upstream commit SHA1 provided is correct: d2408e043e7296017420aa5929b3bba4d5e61013

WARNING: Author mismatch between patch and upstream commit:
Backport author: Pawan Gupta<pawan.kumar.gupta@linux.intel.com>
Commit author: Borislav Petkov (AMD)<bp@alien8.de>

Status in newer kernel trees:
6.14.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)
6.6.y | Present (exact SHA1)

Found fixes commits:
4ba89dd6ddec x86/alternatives: Remove faulty optimization

Note: The patch differs from the upstream commit:
---
1:  d2408e043e729 < -:  ------------- x86/alternative: Optimize returns patching
-:  ------------- > 1:  02b72ccb5f9df Linux 6.1.138
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.1.y        |  Success    |  Success   |

Re: [PATCH 6.1 3/3] x86/its: Fix build errors when CONFIG_MODULES=n

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 9f35e33144ae5377d6a8de86dd3bd4d995c6ac65

WARNING: Author mismatch between patch and upstream commit:
Backport author: Pawan Gupta<pawan.kumar.gupta@linux.intel.com>
Commit author: Eric Biggers<ebiggers@google.com>

Status in newer kernel trees:
6.14.y | Not found
6.12.y | Not found
6.6.y | Not found

Note: The patch differs from the upstream commit:
---
1:  9f35e33144ae5 < -:  ------------- x86/its: Fix build errors when CONFIG_MODULES=n
-:  ------------- > 1:  02b72ccb5f9df Linux 6.1.138
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.6.y        |  Success    |  Success   |

Re: [PATCH 6.1 2/3] x86/alternatives: Remove faulty optimization

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 4ba89dd6ddeca2a733bdaed7c9a5cbe4e19d9124

WARNING: Author mismatch between patch and upstream commit:
Backport author: Pawan Gupta<pawan.kumar.gupta@linux.intel.com>
Commit author: Josh Poimboeuf<jpoimboe@kernel.org>

Status in newer kernel trees:
6.14.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)
6.6.y | Present (exact SHA1)

Note: The patch differs from the upstream commit:
---
1:  4ba89dd6ddeca < -:  ------------- x86/alternatives: Remove faulty optimization
-:  ------------- > 1:  02b72ccb5f9df Linux 6.1.138
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-6.6.y        |  Success    |  Success   |