[PATCH 0/4] x86/alternatives: Do NOPs optimization on a temporary buffer

[PATCH 0/4] x86/alternatives: Do NOPs optimization on a temporary buffer

[Borislav Petkov]

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

Hi,

here's a small set which sprang out from my reacting to the fact that
NOPs optimization in the alternatives code needs to happen on
a temporary buffer like the other alternative operations - not in-place
and cause all kinds of fun.

The result is this, which makes the alternatives code simpler and it is
a net win, size-wise:

 1 file changed, 50 insertions(+), 72 deletions(-)


Constructive feedback is always welcome!

Thx.

Borislav Petkov (AMD) (4):
  x86/alternatives: Use a temporary buffer when optimizing NOPs
  x86/alternatives: Get rid of __optimize_nops()
  x86/alternatives: Optimize optimize_nops()
  x86/alternatives: Sort local vars in apply_alternatives()

 arch/x86/kernel/alternative.c | 122 ++++++++++++++--------------------
 1 file changed, 50 insertions(+), 72 deletions(-)

-- 
2.43.0

[PATCH 1/4] x86/alternatives: Use a temporary buffer when optimizing NOPs

[Borislav Petkov]

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

Instead of optimizing NOPs inplace, use a temporary buffer like the
usual alternatives patching flow does. This obviates the need to grab
locks when patching, see

  6778977590da ("x86/alternatives: Disable interrupts and sync when optimizing NOPs in place")

While at it, add nomenclature definitions clarifying and simplifying the
naming of function-local variables in the alternatives code.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/kernel/alternative.c | 78 +++++++++++++++++++----------------
 1 file changed, 42 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index cc130b57542a..d633eb59f2b6 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -124,6 +124,20 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
 #endif
 };
 
+/*
+ * Nomenclature for variable names to simplify and clarify this code and ease
+ * any potential staring at it:
+ *
+ * @instr: source address of the original instructions in the kernel text as
+ * generated by the compiler.
+ *
+ * @buf: temporary buffer on which the patching operates. This buffer is
+ * eventually text-poked into the kernel image.
+ *
+ * @replacement: pointer to the opcodes which are replacing @instr, located in
+ * the .altinstr_replacement section.
+ */
+
 /*
  * Fill the buffer with a single effective instruction of size @len.
  *
@@ -133,28 +147,28 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
  * each single-byte NOPs). If @len to fill out is > ASM_NOP_MAX, pad with INT3 and
  * *jump* over instead of executing long and daft NOPs.
  */
-static void __init_or_module add_nop(u8 *instr, unsigned int len)
+static void __init_or_module add_nop(u8 *buf, unsigned int len)
 {
-	u8 *target = instr + len;
+	u8 *target = buf + len;
 
 	if (!len)
 		return;
 
 	if (len <= ASM_NOP_MAX) {
-		memcpy(instr, x86_nops[len], len);
+		memcpy(buf, x86_nops[len], len);
 		return;
 	}
 
 	if (len < 128) {
-		__text_gen_insn(instr, JMP8_INSN_OPCODE, instr, target, JMP8_INSN_SIZE);
-		instr += JMP8_INSN_SIZE;
+		__text_gen_insn(buf, JMP8_INSN_OPCODE, buf, target, JMP8_INSN_SIZE);
+		buf += JMP8_INSN_SIZE;
 	} else {
-		__text_gen_insn(instr, JMP32_INSN_OPCODE, instr, target, JMP32_INSN_SIZE);
-		instr += JMP32_INSN_SIZE;
+		__text_gen_insn(buf, JMP32_INSN_OPCODE, buf, target, JMP32_INSN_SIZE);
+		buf += JMP32_INSN_SIZE;
 	}
 
-	for (;instr < target; instr++)
-		*instr = INT3_INSN_OPCODE;
+	for (;buf < target; buf++)
+		*buf = INT3_INSN_OPCODE;
 }
 
 extern s32 __retpoline_sites[], __retpoline_sites_end[];
@@ -187,12 +201,12 @@ static bool insn_is_nop(struct insn *insn)
  * Find the offset of the first non-NOP instruction starting at @offset
  * but no further than @len.
  */
-static int skip_nops(u8 *instr, int offset, int len)
+static int skip_nops(u8 *buf, int offset, int len)
 {
 	struct insn insn;
 
 	for (; offset < len; offset += insn.length) {
-		if (insn_decode_kernel(&insn, &instr[offset]))
+		if (insn_decode_kernel(&insn, &buf[offset]))
 			break;
 
 		if (!insn_is_nop(&insn))
@@ -207,7 +221,7 @@ static int skip_nops(u8 *instr, int offset, int len)
  * to the end of the NOP sequence into a single NOP.
  */
 static bool __init_or_module
-__optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, int *target)
+__optimize_nops(const u8 * const instr, u8 *buf, size_t len, struct insn *insn, int *next, int *prev, int *target)
 {
 	int i = *next - insn->length;
 
@@ -222,12 +236,12 @@ __optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev,
 	if (insn_is_nop(insn)) {
 		int nop = i;
 
-		*next = skip_nops(instr, *next, len);
+		*next = skip_nops(buf, *next, len);
 		if (*target && *next == *target)
 			nop = *prev;
 
-		add_nop(instr + nop, *next - nop);
-		DUMP_BYTES(ALT, instr, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
+		add_nop(buf + nop, *next - nop);
+		DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
 		return true;
 	}
 
@@ -239,32 +253,22 @@ __optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev,
  * "noinline" to cause control flow change and thus invalidate I$ and
  * cause refetch after modification.
  */
-static void __init_or_module noinline optimize_nops(u8 *instr, size_t len)
+static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
 {
 	int prev, target = 0;
 
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
-		if (insn_decode_kernel(&insn, &instr[i]))
+		if (insn_decode_kernel(&insn, &buf[i]))
 			return;
 
 		next = i + insn.length;
 
-		__optimize_nops(instr, len, &insn, &next, &prev, &target);
+		__optimize_nops(instr, buf, len, &insn, &next, &prev, &target);
 	}
 }
 
-static void __init_or_module noinline optimize_nops_inplace(u8 *instr, size_t len)
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	optimize_nops(instr, len);
-	sync_core();
-	local_irq_restore(flags);
-}
-
 /*
  * In this context, "source" is where the instructions are placed in the
  * section .altinstr_replacement, for example during kernel build by the
@@ -336,7 +340,7 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 }
 
 static void __init_or_module noinline
-apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
+apply_relocation(const u8 * const instr, u8 *buf, size_t len, u8 *src, size_t src_len)
 {
 	int prev, target = 0;
 
@@ -348,7 +352,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 
 		next = i + insn.length;
 
-		if (__optimize_nops(buf, len, &insn, &next, &prev, &target))
+		if (__optimize_nops(instr, buf, len, &insn, &next, &prev, &target))
 			continue;
 
 		switch (insn.opcode.bytes[0]) {
@@ -365,7 +369,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 			if (need_reloc(next + insn.immediate.value, src, src_len)) {
 				apply_reloc(insn.immediate.nbytes,
 					    buf + i + insn_offset_immediate(&insn),
-					    src - dest);
+					    src - instr);
 			}
 
 			/*
@@ -373,7 +377,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 			 */
 			if (insn.opcode.bytes[0] == JMP32_INSN_OPCODE) {
 				s32 imm = insn.immediate.value;
-				imm += src - dest;
+				imm += src - instr;
 				imm += JMP32_INSN_SIZE - JMP8_INSN_SIZE;
 				if ((imm >> 31) == (imm >> 7)) {
 					buf[i+0] = JMP8_INSN_OPCODE;
@@ -389,7 +393,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 			if (need_reloc(next + insn.displacement.value, src, src_len)) {
 				apply_reloc(insn.displacement.nbytes,
 					    buf + i + insn_offset_displacement(&insn),
-					    src - dest);
+					    src - instr);
 			}
 		}
 	}
@@ -505,7 +509,9 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		 *   patch if feature is *NOT* present.
 		 */
 		if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
-			optimize_nops_inplace(instr, a->instrlen);
+			memcpy(insn_buff, instr, a->instrlen);
+			optimize_nops(instr, insn_buff, a->instrlen);
+			text_poke_early(instr, insn_buff, a->instrlen);
 			continue;
 		}
 
@@ -527,7 +533,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		for (; insn_buff_sz < a->instrlen; insn_buff_sz++)
 			insn_buff[insn_buff_sz] = 0x90;
 
-		apply_relocation(insn_buff, a->instrlen, instr, replacement, a->replacementlen);
+		apply_relocation(instr, insn_buff, a->instrlen, replacement, a->replacementlen);
 
 		DUMP_BYTES(ALT, instr, a->instrlen, "%px:   old_insn: ", instr);
 		DUMP_BYTES(ALT, replacement, a->replacementlen, "%px:   rpl_insn: ", replacement);
@@ -762,7 +768,7 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
 
 		len = patch_retpoline(addr, &insn, bytes);
 		if (len == insn.length) {
-			optimize_nops(bytes, len);
+			optimize_nops(addr, bytes, len);
 			DUMP_BYTES(RETPOLINE, ((u8*)addr),  len, "%px: orig: ", addr);
 			DUMP_BYTES(RETPOLINE, ((u8*)bytes), len, "%px: repl: ", addr);
 			text_poke_early(addr, bytes, len);
-- 
2.43.0

[PATCH 2/4] x86/alternatives: Get rid of __optimize_nops()

[Borislav Petkov]

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

There's no need to carve out bits of the NOP optimization functionality
and look at JMP opcodes - simply do one more NOPs optimization pass
at the end of the patching.

A lot simpler code.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/alternative.c | 52 +++++++----------------------------
 1 file changed, 10 insertions(+), 42 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index d633eb59f2b6..2dd1c7fe0949 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -216,47 +216,12 @@ static int skip_nops(u8 *buf, int offset, int len)
 	return offset;
 }
 
-/*
- * Optimize a sequence of NOPs, possibly preceded by an unconditional jump
- * to the end of the NOP sequence into a single NOP.
- */
-static bool __init_or_module
-__optimize_nops(const u8 * const instr, u8 *buf, size_t len, struct insn *insn, int *next, int *prev, int *target)
-{
-	int i = *next - insn->length;
-
-	switch (insn->opcode.bytes[0]) {
-	case JMP8_INSN_OPCODE:
-	case JMP32_INSN_OPCODE:
-		*prev = i;
-		*target = *next + insn->immediate.value;
-		return false;
-	}
-
-	if (insn_is_nop(insn)) {
-		int nop = i;
-
-		*next = skip_nops(buf, *next, len);
-		if (*target && *next == *target)
-			nop = *prev;
-
-		add_nop(buf + nop, *next - nop);
-		DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
-		return true;
-	}
-
-	*target = 0;
-	return false;
-}
-
 /*
  * "noinline" to cause control flow change and thus invalidate I$ and
  * cause refetch after modification.
  */
 static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
 {
-	int prev, target = 0;
-
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
@@ -265,7 +230,14 @@ static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *
 
 		next = i + insn.length;
 
-		__optimize_nops(instr, buf, len, &insn, &next, &prev, &target);
+		if (insn_is_nop(&insn)) {
+			int nop = i;
+
+			next = skip_nops(buf, next, len);
+
+			add_nop(buf + nop, next - nop);
+			DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, next);
+		}
 	}
 }
 
@@ -342,8 +314,6 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 static void __init_or_module noinline
 apply_relocation(const u8 * const instr, u8 *buf, size_t len, u8 *src, size_t src_len)
 {
-	int prev, target = 0;
-
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
@@ -352,9 +322,6 @@ apply_relocation(const u8 * const instr, u8 *buf, size_t len, u8 *src, size_t sr
 
 		next = i + insn.length;
 
-		if (__optimize_nops(instr, buf, len, &insn, &next, &prev, &target))
-			continue;
-
 		switch (insn.opcode.bytes[0]) {
 		case 0x0f:
 			if (insn.opcode.bytes[1] < 0x80 ||
@@ -533,7 +500,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		for (; insn_buff_sz < a->instrlen; insn_buff_sz++)
 			insn_buff[insn_buff_sz] = 0x90;
 
-		apply_relocation(instr, insn_buff, a->instrlen, replacement, a->replacementlen);
+		apply_relocation(instr, insn_buff, a->instrlen, replacement, insn_buff_sz);
+		optimize_nops(instr, insn_buff, insn_buff_sz);
 
 		DUMP_BYTES(ALT, instr, a->instrlen, "%px:   old_insn: ", instr);
 		DUMP_BYTES(ALT, replacement, a->replacementlen, "%px:   rpl_insn: ", replacement);
-- 
2.43.0

[PATCH 3/4] x86/alternatives: Optimize optimize_nops()

[Borislav Petkov]

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

Return early if NOPs have already been optimized.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/alternative.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 2dd1c7fe0949..68ee46c379c1 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -233,6 +233,10 @@ static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *
 		if (insn_is_nop(&insn)) {
 			int nop = i;
 
+			/* Has the NOP already been optimized? */
+			if (i + insn.length == len)
+				return;
+
 			next = skip_nops(buf, next, len);
 
 			add_nop(buf + nop, next - nop);
-- 
2.43.0

[PATCH 4/4] x86/alternatives: Sort local vars in apply_alternatives()

[Borislav Petkov]

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

In a reverse x-mas tree.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
 arch/x86/kernel/alternative.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 68ee46c379c1..ee0f681ae107 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -440,9 +440,9 @@ static int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a)
 void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 						  struct alt_instr *end)
 {
-	struct alt_instr *a;
-	u8 *instr, *replacement;
 	u8 insn_buff[MAX_PATCH_LEN];
+	u8 *instr, *replacement;
+	struct alt_instr *a;
 
 	DPRINTK(ALT, "alt table %px, -> %px", start, end);
 
-- 
2.43.0

Re: [PATCH 0/4] x86/alternatives: Do NOPs optimization on a temporary buffer

[Paul Gortmaker]

[[PATCH 0/4] x86/alternatives: Do NOPs optimization on a temporary buffer] On 30/01/2024 (Tue 11:59) Borislav Petkov wrote:

> From: "Borislav Petkov (AMD)" <bp@alien8.de>
> 
> Hi,
> 
> here's a small set which sprang out from my reacting to the fact that
> NOPs optimization in the alternatives code needs to happen on
> a temporary buffer like the other alternative operations - not in-place
> and cause all kinds of fun.
> 
> The result is this, which makes the alternatives code simpler and it is
> a net win, size-wise:
> 
>  1 file changed, 50 insertions(+), 72 deletions(-)
> 
> 
> Constructive feedback is always welcome!

So, I figured I would set up the same reproducer, on the same machine;
build and test a known broken NOP rewrite kernel like v6.5.0 to confirm
I could still reproduce the boot fail in approximately 2% of runs.  And
then move to testing this series.

Well, much to my annoyance my plan broke down at step one.  After about
three hours and over 400 runs, I didn't get a single fail. I still had a
known broken build from the original reporting in October of v6.5.7, so
I let that run for over 300 iterations, and also didn't get any
failures.

I have to assume that even though I'm using the same host, same scripts,
that because I was testing on Yocto master, other things have changed
since October - maybe binutils, qemu, the runqemu script,  ...  In
theory, I could try and reset Yocto back to October-ish but that is
probably of diminishing returns.  And I can't unwind the host machine
distro updates that have happened since October.

With hindsight and knowledge of what the issue was and how narrow the
window was to trigger it, I guess this shouldn't be a surprise.

So as a "next best" effort, I let this rc1-alt-v2 branch run overnight,
and after over 2200 iterations, I didn't get any boot fails.

Paul.
--

> 
> Thx.
> 
> Borislav Petkov (AMD) (4):
>   x86/alternatives: Use a temporary buffer when optimizing NOPs
>   x86/alternatives: Get rid of __optimize_nops()
>   x86/alternatives: Optimize optimize_nops()
>   x86/alternatives: Sort local vars in apply_alternatives()
> 
>  arch/x86/kernel/alternative.c | 122 ++++++++++++++--------------------
>  1 file changed, 50 insertions(+), 72 deletions(-)
> 
> -- 
> 2.43.0
> 

Re: [PATCH 0/4] x86/alternatives: Do NOPs optimization on a temporary buffer

[Borislav Petkov]

On Wed, Jan 31, 2024 at 11:17:27AM -0500, Paul Gortmaker wrote:
> So as a "next best" effort, I let this rc1-alt-v2 branch run overnight,
> and after over 2200 iterations, I didn't get any boot fails.

Thanks a lot!

As mentioned on IRC yesterday, the important thing is that this doesn't
break any of your guests. And that is good enough.

Much appreciated, thanks again!

-- 
Regards/Gruss,
    Boris.

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

[tip: x86/alternatives] x86/alternatives: Sort local vars in apply_alternatives()

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     cadb7de3170e22893b617276c297216039aad88d
Gitweb:        https://git.kernel.org/tip/cadb7de3170e22893b617276c297216039aad88d
Author:        Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate:    Tue, 30 Jan 2024 11:59:41 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 13 Feb 2024 16:27:46 +01:00

x86/alternatives: Sort local vars in apply_alternatives()

In a reverse x-mas tree.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-5-bp@alien8.de
---
 arch/x86/kernel/alternative.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 1ceaaab..9aaf703 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -440,9 +440,9 @@ static int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a)
 void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 						  struct alt_instr *end)
 {
-	struct alt_instr *a;
-	u8 *instr, *replacement;
 	u8 insn_buff[MAX_PATCH_LEN];
+	u8 *instr, *replacement;
+	struct alt_instr *a;
 
 	DPRINTK(ALT, "alt table %px, -> %px", start, end);
 

[tip: x86/alternatives] x86/alternatives: Optimize optimize_nops()

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     f7045230fa2933bf3b38c9c92b5ba46486ef33f9
Gitweb:        https://git.kernel.org/tip/f7045230fa2933bf3b38c9c92b5ba46486ef33f9
Author:        Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate:    Tue, 30 Jan 2024 11:59:40 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 13 Feb 2024 16:26:56 +01:00

x86/alternatives: Optimize optimize_nops()

Return early if NOPs have already been optimized.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-4-bp@alien8.de
---
 arch/x86/kernel/alternative.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index cdbece3..1ceaaab 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -233,6 +233,10 @@ static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *
 		if (insn_is_nop(&insn)) {
 			int nop = i;
 
+			/* Has the NOP already been optimized? */
+			if (i + insn.length == len)
+				return;
+
 			next = skip_nops(buf, next, len);
 
 			add_nop(buf + nop, next - nop);

[tip: x86/alternatives] x86/alternatives: Get rid of __optimize_nops()

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     f9265b75648165f61467a7ea3c9bbae33be7ce27
Gitweb:        https://git.kernel.org/tip/f9265b75648165f61467a7ea3c9bbae33be7ce27
Author:        Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate:    Tue, 30 Jan 2024 11:59:39 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 13 Feb 2024 16:25:46 +01:00

x86/alternatives: Get rid of __optimize_nops()

There's no need to carve out bits of the NOP optimization functionality
and look at JMP opcodes - simply do one more NOPs optimization pass
at the end of patching.

A lot simpler code.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-3-bp@alien8.de
---
 arch/x86/kernel/alternative.c | 52 ++++++----------------------------
 1 file changed, 10 insertions(+), 42 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 835e343..cdbece3 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -217,46 +217,11 @@ static int skip_nops(u8 *buf, int offset, int len)
 }
 
 /*
- * Optimize a sequence of NOPs, possibly preceded by an unconditional jump
- * to the end of the NOP sequence into a single NOP.
- */
-static bool __init_or_module
-__optimize_nops(const u8 * const instr, u8 *buf, size_t len, struct insn *insn, int *next, int *prev, int *target)
-{
-	int i = *next - insn->length;
-
-	switch (insn->opcode.bytes[0]) {
-	case JMP8_INSN_OPCODE:
-	case JMP32_INSN_OPCODE:
-		*prev = i;
-		*target = *next + insn->immediate.value;
-		return false;
-	}
-
-	if (insn_is_nop(insn)) {
-		int nop = i;
-
-		*next = skip_nops(buf, *next, len);
-		if (*target && *next == *target)
-			nop = *prev;
-
-		add_nop(buf + nop, *next - nop);
-		DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
-		return true;
-	}
-
-	*target = 0;
-	return false;
-}
-
-/*
  * "noinline" to cause control flow change and thus invalidate I$ and
  * cause refetch after modification.
  */
 static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
 {
-	int prev, target = 0;
-
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
@@ -265,7 +230,14 @@ static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *
 
 		next = i + insn.length;
 
-		__optimize_nops(instr, buf, len, &insn, &next, &prev, &target);
+		if (insn_is_nop(&insn)) {
+			int nop = i;
+
+			next = skip_nops(buf, next, len);
+
+			add_nop(buf + nop, next - nop);
+			DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, next);
+		}
 	}
 }
 
@@ -342,8 +314,6 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 static void __init_or_module noinline
 apply_relocation(const u8 * const instr, u8 *buf, size_t len, u8 *src, size_t src_len)
 {
-	int prev, target = 0;
-
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
@@ -352,9 +322,6 @@ apply_relocation(const u8 * const instr, u8 *buf, size_t len, u8 *src, size_t sr
 
 		next = i + insn.length;
 
-		if (__optimize_nops(instr, buf, len, &insn, &next, &prev, &target))
-			continue;
-
 		switch (insn.opcode.bytes[0]) {
 		case 0x0f:
 			if (insn.opcode.bytes[1] < 0x80 ||
@@ -533,7 +500,8 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		for (; insn_buff_sz < a->instrlen; insn_buff_sz++)
 			insn_buff[insn_buff_sz] = 0x90;
 
-		apply_relocation(instr, insn_buff, a->instrlen, replacement, a->replacementlen);
+		apply_relocation(instr, insn_buff, a->instrlen, replacement, insn_buff_sz);
+		optimize_nops(instr, insn_buff, insn_buff_sz);
 
 		DUMP_BYTES(ALT, instr, a->instrlen, "%px:   old_insn: ", instr);
 		DUMP_BYTES(ALT, replacement, a->replacementlen, "%px:   rpl_insn: ", replacement);

[tip: x86/alternatives] x86/alternatives: Use a temporary buffer when optimizing NOPs

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     fca88864f9d5637381b71a0cd38b7f5e82eab01d
Gitweb:        https://git.kernel.org/tip/fca88864f9d5637381b71a0cd38b7f5e82eab01d
Author:        Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate:    Tue, 30 Jan 2024 11:59:38 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 13 Feb 2024 16:16:02 +01:00

x86/alternatives: Use a temporary buffer when optimizing NOPs

Instead of optimizing NOPs in-place, use a temporary buffer like the
usual alternatives patching flow does. This obviates the need to grab
locks when patching, see

  6778977590da ("x86/alternatives: Disable interrupts and sync when optimizing NOPs in place")

While at it, add nomenclature definitions clarifying and simplifying the
naming of function-local variables in the alternatives code.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240130105941.19707-2-bp@alien8.de
---
 arch/x86/kernel/alternative.c | 78 ++++++++++++++++++----------------
 1 file changed, 42 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 1d85cb7..835e343 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -125,6 +125,20 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
 };
 
 /*
+ * Nomenclature for variable names to simplify and clarify this code and ease
+ * any potential staring at it:
+ *
+ * @instr: source address of the original instructions in the kernel text as
+ * generated by the compiler.
+ *
+ * @buf: temporary buffer on which the patching operates. This buffer is
+ * eventually text-poked into the kernel image.
+ *
+ * @replacement: pointer to the opcodes which are replacing @instr, located in
+ * the .altinstr_replacement section.
+ */
+
+/*
  * Fill the buffer with a single effective instruction of size @len.
  *
  * In order not to issue an ORC stack depth tracking CFI entry (Call Frame Info)
@@ -133,28 +147,28 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
  * each single-byte NOPs). If @len to fill out is > ASM_NOP_MAX, pad with INT3 and
  * *jump* over instead of executing long and daft NOPs.
  */
-static void __init_or_module add_nop(u8 *instr, unsigned int len)
+static void __init_or_module add_nop(u8 *buf, unsigned int len)
 {
-	u8 *target = instr + len;
+	u8 *target = buf + len;
 
 	if (!len)
 		return;
 
 	if (len <= ASM_NOP_MAX) {
-		memcpy(instr, x86_nops[len], len);
+		memcpy(buf, x86_nops[len], len);
 		return;
 	}
 
 	if (len < 128) {
-		__text_gen_insn(instr, JMP8_INSN_OPCODE, instr, target, JMP8_INSN_SIZE);
-		instr += JMP8_INSN_SIZE;
+		__text_gen_insn(buf, JMP8_INSN_OPCODE, buf, target, JMP8_INSN_SIZE);
+		buf += JMP8_INSN_SIZE;
 	} else {
-		__text_gen_insn(instr, JMP32_INSN_OPCODE, instr, target, JMP32_INSN_SIZE);
-		instr += JMP32_INSN_SIZE;
+		__text_gen_insn(buf, JMP32_INSN_OPCODE, buf, target, JMP32_INSN_SIZE);
+		buf += JMP32_INSN_SIZE;
 	}
 
-	for (;instr < target; instr++)
-		*instr = INT3_INSN_OPCODE;
+	for (;buf < target; buf++)
+		*buf = INT3_INSN_OPCODE;
 }
 
 extern s32 __retpoline_sites[], __retpoline_sites_end[];
@@ -187,12 +201,12 @@ static bool insn_is_nop(struct insn *insn)
  * Find the offset of the first non-NOP instruction starting at @offset
  * but no further than @len.
  */
-static int skip_nops(u8 *instr, int offset, int len)
+static int skip_nops(u8 *buf, int offset, int len)
 {
 	struct insn insn;
 
 	for (; offset < len; offset += insn.length) {
-		if (insn_decode_kernel(&insn, &instr[offset]))
+		if (insn_decode_kernel(&insn, &buf[offset]))
 			break;
 
 		if (!insn_is_nop(&insn))
@@ -207,7 +221,7 @@ static int skip_nops(u8 *instr, int offset, int len)
  * to the end of the NOP sequence into a single NOP.
  */
 static bool __init_or_module
-__optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, int *target)
+__optimize_nops(const u8 * const instr, u8 *buf, size_t len, struct insn *insn, int *next, int *prev, int *target)
 {
 	int i = *next - insn->length;
 
@@ -222,12 +236,12 @@ __optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, 
 	if (insn_is_nop(insn)) {
 		int nop = i;
 
-		*next = skip_nops(instr, *next, len);
+		*next = skip_nops(buf, *next, len);
 		if (*target && *next == *target)
 			nop = *prev;
 
-		add_nop(instr + nop, *next - nop);
-		DUMP_BYTES(ALT, instr, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
+		add_nop(buf + nop, *next - nop);
+		DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
 		return true;
 	}
 
@@ -239,32 +253,22 @@ __optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, 
  * "noinline" to cause control flow change and thus invalidate I$ and
  * cause refetch after modification.
  */
-static void __init_or_module noinline optimize_nops(u8 *instr, size_t len)
+static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
 {
 	int prev, target = 0;
 
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
-		if (insn_decode_kernel(&insn, &instr[i]))
+		if (insn_decode_kernel(&insn, &buf[i]))
 			return;
 
 		next = i + insn.length;
 
-		__optimize_nops(instr, len, &insn, &next, &prev, &target);
+		__optimize_nops(instr, buf, len, &insn, &next, &prev, &target);
 	}
 }
 
-static void __init_or_module noinline optimize_nops_inplace(u8 *instr, size_t len)
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	optimize_nops(instr, len);
-	sync_core();
-	local_irq_restore(flags);
-}
-
 /*
  * In this context, "source" is where the instructions are placed in the
  * section .altinstr_replacement, for example during kernel build by the
@@ -336,7 +340,7 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 }
 
 static void __init_or_module noinline
-apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
+apply_relocation(const u8 * const instr, u8 *buf, size_t len, u8 *src, size_t src_len)
 {
 	int prev, target = 0;
 
@@ -348,7 +352,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 
 		next = i + insn.length;
 
-		if (__optimize_nops(buf, len, &insn, &next, &prev, &target))
+		if (__optimize_nops(instr, buf, len, &insn, &next, &prev, &target))
 			continue;
 
 		switch (insn.opcode.bytes[0]) {
@@ -365,7 +369,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 			if (need_reloc(next + insn.immediate.value, src, src_len)) {
 				apply_reloc(insn.immediate.nbytes,
 					    buf + i + insn_offset_immediate(&insn),
-					    src - dest);
+					    src - instr);
 			}
 
 			/*
@@ -373,7 +377,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 			 */
 			if (insn.opcode.bytes[0] == JMP32_INSN_OPCODE) {
 				s32 imm = insn.immediate.value;
-				imm += src - dest;
+				imm += src - instr;
 				imm += JMP32_INSN_SIZE - JMP8_INSN_SIZE;
 				if ((imm >> 31) == (imm >> 7)) {
 					buf[i+0] = JMP8_INSN_OPCODE;
@@ -389,7 +393,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 			if (need_reloc(next + insn.displacement.value, src, src_len)) {
 				apply_reloc(insn.displacement.nbytes,
 					    buf + i + insn_offset_displacement(&insn),
-					    src - dest);
+					    src - instr);
 			}
 		}
 	}
@@ -505,7 +509,9 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		 *   patch if feature is *NOT* present.
 		 */
 		if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
-			optimize_nops_inplace(instr, a->instrlen);
+			memcpy(insn_buff, instr, a->instrlen);
+			optimize_nops(instr, insn_buff, a->instrlen);
+			text_poke_early(instr, insn_buff, a->instrlen);
 			continue;
 		}
 
@@ -527,7 +533,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		for (; insn_buff_sz < a->instrlen; insn_buff_sz++)
 			insn_buff[insn_buff_sz] = 0x90;
 
-		apply_relocation(insn_buff, a->instrlen, instr, replacement, a->replacementlen);
+		apply_relocation(instr, insn_buff, a->instrlen, replacement, a->replacementlen);
 
 		DUMP_BYTES(ALT, instr, a->instrlen, "%px:   old_insn: ", instr);
 		DUMP_BYTES(ALT, replacement, a->replacementlen, "%px:   rpl_insn: ", replacement);
@@ -762,7 +768,7 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
 
 		len = patch_retpoline(addr, &insn, bytes);
 		if (len == insn.length) {
-			optimize_nops(bytes, len);
+			optimize_nops(addr, bytes, len);
 			DUMP_BYTES(RETPOLINE, ((u8*)addr),  len, "%px: orig: ", addr);
 			DUMP_BYTES(RETPOLINE, ((u8*)bytes), len, "%px: repl: ", addr);
 			text_poke_early(addr, bytes, len);

[tip: x86/alternatives] x86/alternatives: Sort local vars in apply_alternatives()

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     05d277c9a9023e11d2f30a994bde08b854af52a0
Gitweb:        https://git.kernel.org/tip/05d277c9a9023e11d2f30a994bde08b854af52a0
Author:        Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate:    Tue, 30 Jan 2024 11:59:41 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 09 Apr 2024 18:16:57 +02:00

x86/alternatives: Sort local vars in apply_alternatives()

In a reverse x-mas tree.

No functional changes.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-5-bp@alien8.de
---
 arch/x86/kernel/alternative.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 67dd7c3..7555c15 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -445,9 +445,9 @@ static int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a)
 void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 						  struct alt_instr *end)
 {
-	struct alt_instr *a;
-	u8 *instr, *replacement;
 	u8 insn_buff[MAX_PATCH_LEN];
+	u8 *instr, *replacement;
+	struct alt_instr *a;
 
 	DPRINTK(ALT, "alt table %px, -> %px", start, end);
 

[tip: x86/alternatives] x86/alternatives: Optimize optimize_nops()

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     c3a3cb5c3d893d7ca75c773ddd107832f13e7b57
Gitweb:        https://git.kernel.org/tip/c3a3cb5c3d893d7ca75c773ddd107832f13e7b57
Author:        Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate:    Tue, 30 Jan 2024 11:59:40 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 09 Apr 2024 18:15:03 +02:00

x86/alternatives: Optimize optimize_nops()

Return early if NOPs have already been optimized.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-4-bp@alien8.de
---
 arch/x86/kernel/alternative.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 4b3378c..67dd7c3 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -233,6 +233,10 @@ static void noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
 		if (insn_is_nop(&insn)) {
 			int nop = i;
 
+			/* Has the NOP already been optimized? */
+			if (i + insn.length == len)
+				return;
+
 			next = skip_nops(buf, next, len);
 
 			add_nop(buf + nop, next - nop);

[tip: x86/alternatives] x86/alternatives: Get rid of __optimize_nops()

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     da8f9cf7e721c690ca169fa88641a6c4cee5cae4
Gitweb:        https://git.kernel.org/tip/da8f9cf7e721c690ca169fa88641a6c4cee5cae4
Author:        Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate:    Tue, 30 Jan 2024 11:59:39 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 09 Apr 2024 18:12:53 +02:00

x86/alternatives: Get rid of __optimize_nops()

There's no need to carve out bits of the NOP optimization functionality
and look at JMP opcodes - simply do one more NOPs optimization pass
at the end of patching.

A lot simpler code.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-3-bp@alien8.de
---
 arch/x86/kernel/alternative.c | 59 +++++++++-------------------------
 1 file changed, 16 insertions(+), 43 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index ec94f13..4b3378c 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -217,46 +217,11 @@ static int skip_nops(u8 *buf, int offset, int len)
 }
 
 /*
- * Optimize a sequence of NOPs, possibly preceded by an unconditional jump
- * to the end of the NOP sequence into a single NOP.
- */
-static bool
-__optimize_nops(const u8 * const instr, u8 *buf, size_t len, struct insn *insn, int *next, int *prev, int *target)
-{
-	int i = *next - insn->length;
-
-	switch (insn->opcode.bytes[0]) {
-	case JMP8_INSN_OPCODE:
-	case JMP32_INSN_OPCODE:
-		*prev = i;
-		*target = *next + insn->immediate.value;
-		return false;
-	}
-
-	if (insn_is_nop(insn)) {
-		int nop = i;
-
-		*next = skip_nops(buf, *next, len);
-		if (*target && *next == *target)
-			nop = *prev;
-
-		add_nop(buf + nop, *next - nop);
-		DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
-		return true;
-	}
-
-	*target = 0;
-	return false;
-}
-
-/*
  * "noinline" to cause control flow change and thus invalidate I$ and
  * cause refetch after modification.
  */
-static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
+static void noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
 {
-	int prev, target = 0;
-
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
@@ -265,7 +230,14 @@ static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *
 
 		next = i + insn.length;
 
-		__optimize_nops(instr, buf, len, &insn, &next, &prev, &target);
+		if (insn_is_nop(&insn)) {
+			int nop = i;
+
+			next = skip_nops(buf, next, len);
+
+			add_nop(buf + nop, next - nop);
+			DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, next);
+		}
 	}
 }
 
@@ -339,10 +311,8 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 	return (target < src || target > src + src_len);
 }
 
-void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
+static void __apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
 {
-	int prev, target = 0;
-
 	for (int next, i = 0; i < instrlen; i = next) {
 		struct insn insn;
 
@@ -351,9 +321,6 @@ void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl
 
 		next = i + insn.length;
 
-		if (__optimize_nops(instr, buf, instrlen, &insn, &next, &prev, &target))
-			continue;
-
 		switch (insn.opcode.bytes[0]) {
 		case 0x0f:
 			if (insn.opcode.bytes[1] < 0x80 ||
@@ -398,6 +365,12 @@ void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl
 	}
 }
 
+void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
+{
+	__apply_relocation(buf, instr, instrlen, repl, repl_len);
+	optimize_nops(instr, buf, repl_len);
+}
+
 /* Low-level backend functions usable from alternative code replacements. */
 DEFINE_ASM_FUNC(nop_func, "", .entry.text);
 EXPORT_SYMBOL_GPL(nop_func);

[tip: x86/alternatives] x86/alternatives: Use a temporary buffer when optimizing NOPs

[tip-bot2 for Borislav Petkov (AMD)]

The following commit has been merged into the x86/alternatives branch of tip:

Commit-ID:     f796c75837623058db1ff93252b9f1681306b83d
Gitweb:        https://git.kernel.org/tip/f796c75837623058db1ff93252b9f1681306b83d
Author:        Borislav Petkov (AMD) <bp@alien8.de>
AuthorDate:    Tue, 30 Jan 2024 11:59:38 +01:00
Committer:     Borislav Petkov (AMD) <bp@alien8.de>
CommitterDate: Tue, 09 Apr 2024 18:08:11 +02:00

x86/alternatives: Use a temporary buffer when optimizing NOPs

Instead of optimizing NOPs in-place, use a temporary buffer like the
usual alternatives patching flow does. This obviates the need to grab
locks when patching, see

  6778977590da ("x86/alternatives: Disable interrupts and sync when optimizing NOPs in place")

While at it, add nomenclature definitions clarifying and simplifying the
naming of function-local variables in the alternatives code.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20240130105941.19707-2-bp@alien8.de
---
 arch/x86/include/asm/text-patching.h |  2 +-
 arch/x86/kernel/alternative.c        | 84 ++++++++++++++-------------
 arch/x86/kernel/callthunks.c         |  9 +--
 3 files changed, 49 insertions(+), 46 deletions(-)

diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h
index 345aafb..6259f19 100644
--- a/arch/x86/include/asm/text-patching.h
+++ b/arch/x86/include/asm/text-patching.h
@@ -15,7 +15,7 @@
 
 extern void text_poke_early(void *addr, const void *opcode, size_t len);
 
-extern void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len);
+extern void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len);
 
 /*
  * Clear and restore the kernel write-protection flag on the local CPU.
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 45a280f..ec94f13 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -125,6 +125,20 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
 };
 
 /*
+ * Nomenclature for variable names to simplify and clarify this code and ease
+ * any potential staring at it:
+ *
+ * @instr: source address of the original instructions in the kernel text as
+ * generated by the compiler.
+ *
+ * @buf: temporary buffer on which the patching operates. This buffer is
+ * eventually text-poked into the kernel image.
+ *
+ * @replacement/@repl: pointer to the opcodes which are replacing @instr, located
+ * in the .altinstr_replacement section.
+ */
+
+/*
  * Fill the buffer with a single effective instruction of size @len.
  *
  * In order not to issue an ORC stack depth tracking CFI entry (Call Frame Info)
@@ -133,28 +147,28 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
  * each single-byte NOPs). If @len to fill out is > ASM_NOP_MAX, pad with INT3 and
  * *jump* over instead of executing long and daft NOPs.
  */
-static void add_nop(u8 *instr, unsigned int len)
+static void add_nop(u8 *buf, unsigned int len)
 {
-	u8 *target = instr + len;
+	u8 *target = buf + len;
 
 	if (!len)
 		return;
 
 	if (len <= ASM_NOP_MAX) {
-		memcpy(instr, x86_nops[len], len);
+		memcpy(buf, x86_nops[len], len);
 		return;
 	}
 
 	if (len < 128) {
-		__text_gen_insn(instr, JMP8_INSN_OPCODE, instr, target, JMP8_INSN_SIZE);
-		instr += JMP8_INSN_SIZE;
+		__text_gen_insn(buf, JMP8_INSN_OPCODE, buf, target, JMP8_INSN_SIZE);
+		buf += JMP8_INSN_SIZE;
 	} else {
-		__text_gen_insn(instr, JMP32_INSN_OPCODE, instr, target, JMP32_INSN_SIZE);
-		instr += JMP32_INSN_SIZE;
+		__text_gen_insn(buf, JMP32_INSN_OPCODE, buf, target, JMP32_INSN_SIZE);
+		buf += JMP32_INSN_SIZE;
 	}
 
-	for (;instr < target; instr++)
-		*instr = INT3_INSN_OPCODE;
+	for (;buf < target; buf++)
+		*buf = INT3_INSN_OPCODE;
 }
 
 extern s32 __retpoline_sites[], __retpoline_sites_end[];
@@ -187,12 +201,12 @@ static bool insn_is_nop(struct insn *insn)
  * Find the offset of the first non-NOP instruction starting at @offset
  * but no further than @len.
  */
-static int skip_nops(u8 *instr, int offset, int len)
+static int skip_nops(u8 *buf, int offset, int len)
 {
 	struct insn insn;
 
 	for (; offset < len; offset += insn.length) {
-		if (insn_decode_kernel(&insn, &instr[offset]))
+		if (insn_decode_kernel(&insn, &buf[offset]))
 			break;
 
 		if (!insn_is_nop(&insn))
@@ -207,7 +221,7 @@ static int skip_nops(u8 *instr, int offset, int len)
  * to the end of the NOP sequence into a single NOP.
  */
 static bool
-__optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, int *target)
+__optimize_nops(const u8 * const instr, u8 *buf, size_t len, struct insn *insn, int *next, int *prev, int *target)
 {
 	int i = *next - insn->length;
 
@@ -222,12 +236,12 @@ __optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, 
 	if (insn_is_nop(insn)) {
 		int nop = i;
 
-		*next = skip_nops(instr, *next, len);
+		*next = skip_nops(buf, *next, len);
 		if (*target && *next == *target)
 			nop = *prev;
 
-		add_nop(instr + nop, *next - nop);
-		DUMP_BYTES(ALT, instr, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
+		add_nop(buf + nop, *next - nop);
+		DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *next);
 		return true;
 	}
 
@@ -239,32 +253,22 @@ __optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *prev, 
  * "noinline" to cause control flow change and thus invalidate I$ and
  * cause refetch after modification.
  */
-static void __init_or_module noinline optimize_nops(u8 *instr, size_t len)
+static void __init_or_module noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
 {
 	int prev, target = 0;
 
 	for (int next, i = 0; i < len; i = next) {
 		struct insn insn;
 
-		if (insn_decode_kernel(&insn, &instr[i]))
+		if (insn_decode_kernel(&insn, &buf[i]))
 			return;
 
 		next = i + insn.length;
 
-		__optimize_nops(instr, len, &insn, &next, &prev, &target);
+		__optimize_nops(instr, buf, len, &insn, &next, &prev, &target);
 	}
 }
 
-static void __init_or_module noinline optimize_nops_inplace(u8 *instr, size_t len)
-{
-	unsigned long flags;
-
-	local_irq_save(flags);
-	optimize_nops(instr, len);
-	sync_core();
-	local_irq_restore(flags);
-}
-
 /*
  * In this context, "source" is where the instructions are placed in the
  * section .altinstr_replacement, for example during kernel build by the
@@ -335,11 +339,11 @@ bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
 	return (target < src || target > src + src_len);
 }
 
-void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
+void apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
 {
 	int prev, target = 0;
 
-	for (int next, i = 0; i < len; i = next) {
+	for (int next, i = 0; i < instrlen; i = next) {
 		struct insn insn;
 
 		if (WARN_ON_ONCE(insn_decode_kernel(&insn, &buf[i])))
@@ -347,7 +351,7 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 
 		next = i + insn.length;
 
-		if (__optimize_nops(buf, len, &insn, &next, &prev, &target))
+		if (__optimize_nops(instr, buf, instrlen, &insn, &next, &prev, &target))
 			continue;
 
 		switch (insn.opcode.bytes[0]) {
@@ -361,10 +365,10 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 		case JMP8_INSN_OPCODE:
 		case JMP32_INSN_OPCODE:
 		case CALL_INSN_OPCODE:
-			if (need_reloc(next + insn.immediate.value, src, src_len)) {
+			if (need_reloc(next + insn.immediate.value, repl, repl_len)) {
 				apply_reloc(insn.immediate.nbytes,
 					    buf + i + insn_offset_immediate(&insn),
-					    src - dest);
+					    repl - instr);
 			}
 
 			/*
@@ -372,7 +376,7 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 			 */
 			if (insn.opcode.bytes[0] == JMP32_INSN_OPCODE) {
 				s32 imm = insn.immediate.value;
-				imm += src - dest;
+				imm += repl - instr;
 				imm += JMP32_INSN_SIZE - JMP8_INSN_SIZE;
 				if ((imm >> 31) == (imm >> 7)) {
 					buf[i+0] = JMP8_INSN_OPCODE;
@@ -385,10 +389,10 @@ void apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len)
 		}
 
 		if (insn_rip_relative(&insn)) {
-			if (need_reloc(next + insn.displacement.value, src, src_len)) {
+			if (need_reloc(next + insn.displacement.value, repl, repl_len)) {
 				apply_reloc(insn.displacement.nbytes,
 					    buf + i + insn_offset_displacement(&insn),
-					    src - dest);
+					    repl - instr);
 			}
 		}
 	}
@@ -504,7 +508,9 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		 *   patch if feature is *NOT* present.
 		 */
 		if (!boot_cpu_has(a->cpuid) == !(a->flags & ALT_FLAG_NOT)) {
-			optimize_nops_inplace(instr, a->instrlen);
+			memcpy(insn_buff, instr, a->instrlen);
+			optimize_nops(instr, insn_buff, a->instrlen);
+			text_poke_early(instr, insn_buff, a->instrlen);
 			continue;
 		}
 
@@ -526,7 +532,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
 		for (; insn_buff_sz < a->instrlen; insn_buff_sz++)
 			insn_buff[insn_buff_sz] = 0x90;
 
-		apply_relocation(insn_buff, a->instrlen, instr, replacement, a->replacementlen);
+		apply_relocation(insn_buff, instr, a->instrlen, replacement, a->replacementlen);
 
 		DUMP_BYTES(ALT, instr, a->instrlen, "%px:   old_insn: ", instr);
 		DUMP_BYTES(ALT, replacement, a->replacementlen, "%px:   rpl_insn: ", replacement);
@@ -761,7 +767,7 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
 
 		len = patch_retpoline(addr, &insn, bytes);
 		if (len == insn.length) {
-			optimize_nops(bytes, len);
+			optimize_nops(addr, bytes, len);
 			DUMP_BYTES(RETPOLINE, ((u8*)addr),  len, "%px: orig: ", addr);
 			DUMP_BYTES(RETPOLINE, ((u8*)bytes), len, "%px: repl: ", addr);
 			text_poke_early(addr, bytes, len);
diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index e92ff0c..4656474 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -185,8 +185,7 @@ static void *patch_dest(void *dest, bool direct)
 	u8 *pad = dest - tsize;
 
 	memcpy(insn_buff, skl_call_thunk_template, tsize);
-	apply_relocation(insn_buff, tsize, pad,
-			 skl_call_thunk_template, tsize);
+	apply_relocation(insn_buff, pad, tsize, skl_call_thunk_template, tsize);
 
 	/* Already patched? */
 	if (!bcmp(pad, insn_buff, tsize))
@@ -308,8 +307,7 @@ static bool is_callthunk(void *addr)
 	pad = (void *)(dest - tmpl_size);
 
 	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
-	apply_relocation(insn_buff, tmpl_size, pad,
-			 skl_call_thunk_template, tmpl_size);
+	apply_relocation(insn_buff, pad, tmpl_size, skl_call_thunk_template, tmpl_size);
 
 	return !bcmp(pad, insn_buff, tmpl_size);
 }
@@ -327,8 +325,7 @@ int x86_call_depth_emit_accounting(u8 **pprog, void *func, void *ip)
 		return 0;
 
 	memcpy(insn_buff, skl_call_thunk_template, tmpl_size);
-	apply_relocation(insn_buff, tmpl_size, ip,
-			 skl_call_thunk_template, tmpl_size);
+	apply_relocation(insn_buff, ip, tmpl_size, skl_call_thunk_template, tmpl_size);
 
 	memcpy(*pprog, insn_buff, tmpl_size);
 	*pprog += tmpl_size;