linux-kernel - [4.4-stable 18/22] x86/microcode/AMD: Change load_microcode_amd()'s param to bool to fix preemptibility bug

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Date:   Tue, 20 Feb 2018 12:55:05 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     stable@...r.kernel.org
Cc:     Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: [4.4-stable 18/22] x86/microcode/AMD: Change load_microcode_amd()'s param to bool to fix preemptibility bug

From: Borislav Petkov <bp@...e.de>

commit dac6ca243c4c49a9ca7507d3d66140ebfac8b04b upstream.

With CONFIG_DEBUG_PREEMPT enabled, I get:

  BUG: using smp_processor_id() in preemptible [00000000] code: swapper/0/1
  caller is debug_smp_processor_id
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.12.0-rc2+ #2
  Call Trace:
   dump_stack
   check_preemption_disabled
   debug_smp_processor_id
   save_microcode_in_initrd_amd
   ? microcode_init
   save_microcode_in_initrd
   ...

because, well, it says it above, we're using smp_processor_id() in
preemptible code.

But passing the CPU number is not really needed. It is only used to
determine whether we're on the BSP, and, if so, to save the microcode
patch for early loading.

 [ We don't absolutely need to do it on the BSP but we do that
   customarily there. ]

Instead, convert that function parameter to a boolean which denotes
whether the patch should be saved or not, thereby avoiding the use of
smp_processor_id() in preemptible code.

Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20170528200414.31305-1-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@...nel.org>
[arnd: rebased to 4.9, after running into warning:
 arch/x86/kernel/cpu/microcode/amd.c:881:30: self-comparison always evaluates to true]
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/x86/include/asm/microcode_amd.h |  1 -
 arch/x86/kernel/cpu/microcode/amd.c  | 17 +++++++++++------
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/microcode_amd.h b/arch/x86/include/asm/microcode_amd.h
index adfc847a395e..fb163f02ebb1 100644
--- a/arch/x86/include/asm/microcode_amd.h
+++ b/arch/x86/include/asm/microcode_amd.h
@@ -59,7 +59,6 @@ static inline u16 find_equiv_id(struct equiv_cpu_entry *equiv_cpu_table,
 
 extern int __apply_microcode_amd(struct microcode_amd *mc_amd);
 extern int apply_microcode_amd(int cpu);
-extern enum ucode_state load_microcode_amd(int cpu, u8 family, const u8 *data, size_t size);
 
 #define PATCH_MAX_SIZE PAGE_SIZE
 extern u8 amd_ucode_patch[PATCH_MAX_SIZE];
diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
index 2a0f44d225fe..6da6f9cd6d2d 100644
--- a/arch/x86/kernel/cpu/microcode/amd.c
+++ b/arch/x86/kernel/cpu/microcode/amd.c
@@ -131,6 +131,9 @@ static size_t compute_container_size(u8 *data, u32 total_size)
 	return size;
 }
 
+static enum ucode_state
+load_microcode_amd(bool save, u8 family, const u8 *data, size_t size);
+
 /*
  * Early load occurs before we can vmalloc(). So we look for the microcode
  * patch container file in initrd, traverse equivalent cpu table, look for a
@@ -438,7 +441,7 @@ int __init save_microcode_in_initrd_amd(void)
 	eax   = cpuid_eax(0x00000001);
 	eax   = ((eax >> 8) & 0xf) + ((eax >> 20) & 0xff);
 
-	ret = load_microcode_amd(smp_processor_id(), eax, container, container_size);
+	ret = load_microcode_amd(true, eax, container, container_size);
 	if (ret != UCODE_OK)
 		retval = -EINVAL;
 
@@ -854,7 +857,8 @@ static enum ucode_state __load_microcode_amd(u8 family, const u8 *data,
 	return UCODE_OK;
 }
 
-enum ucode_state load_microcode_amd(int cpu, u8 family, const u8 *data, size_t size)
+static enum ucode_state
+load_microcode_amd(bool save, u8 family, const u8 *data, size_t size)
 {
 	enum ucode_state ret;
 
@@ -868,8 +872,8 @@ enum ucode_state load_microcode_amd(int cpu, u8 family, const u8 *data, size_t s
 
 #ifdef CONFIG_X86_32
 	/* save BSP's matching patch for early load */
-	if (cpu_data(cpu).cpu_index == boot_cpu_data.cpu_index) {
-		struct ucode_patch *p = find_patch(cpu);
+	if (save) {
+		struct ucode_patch *p = find_patch(0);
 		if (p) {
 			memset(amd_ucode_patch, 0, PATCH_MAX_SIZE);
 			memcpy(amd_ucode_patch, p->data, min_t(u32, ksize(p->data),
@@ -901,11 +905,12 @@ static enum ucode_state request_microcode_amd(int cpu, struct device *device,
 {
 	char fw_name[36] = "amd-ucode/microcode_amd.bin";
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
+	bool bsp = c->cpu_index == boot_cpu_data.cpu_index;
 	enum ucode_state ret = UCODE_NFOUND;
 	const struct firmware *fw;
 
 	/* reload ucode container only on the boot cpu */
-	if (!refresh_fw || c->cpu_index != boot_cpu_data.cpu_index)
+	if (!refresh_fw || !bsp)
 		return UCODE_OK;
 
 	if (c->x86 >= 0x15)
@@ -922,7 +927,7 @@ static enum ucode_state request_microcode_amd(int cpu, struct device *device,
 		goto fw_release;
 	}
 
-	ret = load_microcode_amd(cpu, c->x86, fw->data, fw->size);
+	ret = load_microcode_amd(bsp, c->x86, fw->data, fw->size);
 
  fw_release:
 	release_firmware(fw);
-- 
2.9.0