[PATCH 0/2] Two x86 fixes

[PATCH 0/2] Two x86 fixes

[Ammar Faizi]

Hi,

Two fixes for x86 arch.

[PATCH 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()`

@bp is a local variable, calling mce_threshold_remove_device() when
threshold_create_bank() fails will not free the @bp. Note that
mce_threshold_remove_device() frees the @bp only if it's already
stored in the @threshold_banks per-CPU variable.

At that point, the @threshold_banks per-CPU variable is still NULL,
so the mce_threshold_remove_device() will just be a no-op and the
@bp is leaked.

Fix this by calling kfree() and early returning when we fail.

This bug is introduced by commit 6458de97fc15530b544 ("x86/mce/amd:
Straighten CPU hotplug path") [1].

Link: https://lore.kernel.org/all/20200403161943.1458-6-bp@alien8.de [1]

[PATCH 2/2] x86/mce/amd: Fix memory leak when `threshold_create_bank()` fails.

@bp is a local variable, calling mce_threshold_remove_device() when
threshold_create_bank() fails will not free the @bp. Note that
mce_threshold_remove_device() frees the @bp only if it's already
stored in the @threshold_banks per-CPU variable.

At that point, the @threshold_banks per-CPU variable is still NULL,
so the mce_threshold_remove_device() will just be a no-op and the
@bp is leaked.

Fix this by calling kfree() and early returning when we fail.

Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---

Ammar Faizi (2):
  x86/delay: Fix the wrong asm constraint in `delay_loop()`
  x86/mce/amd: Fix memory leak when `threshold_create_bank()` fails

 arch/x86/kernel/cpu/mce/amd.c | 9 ++++-----
 arch/x86/lib/delay.c          | 4 ++--
 2 files changed, 6 insertions(+), 7 deletions(-)


base-commit: 7e57714cd0ad2d5bb90e50b5096a0e671dec1ef3
-- 
2.32.0

[PATCH 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()`

[Ammar Faizi]

The asm constraint does not reflect that the asm statement can modify
the value of @loops. But the asm statement in delay_loop() does change
the @loops.

If by any chance the compiler inlines this function, it may clobber
random stuff (e.g. local variable, important temporary value in reg,
etc.).

Fortunately, delay_loop() is only called indirectly (so it can't
inline), and then the register it clobbers is %rax (which is by the
nature of the calling convention, it's a caller saved register), so it
didn't yield any bug.

^ That shouldn't be an excuse for using the wrong constraint anyway.

This changes "a" (as an input) to "+a" (as an input and output).

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Fixes: e01b70ef3eb3080fecc35e15f68cd274c0a48163 ("x86: fix bug in arch/i386/lib/delay.c file, delay_loop function")
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 arch/x86/lib/delay.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/delay.c b/arch/x86/lib/delay.c
index 65d15df6212d..0e65d00e2339 100644
--- a/arch/x86/lib/delay.c
+++ b/arch/x86/lib/delay.c
@@ -54,8 +54,8 @@ static void delay_loop(u64 __loops)
 		"	jnz 2b		\n"
 		"3:	dec %0		\n"
 
-		: /* we don't need output */
-		:"a" (loops)
+		: "+a" (loops)
+		:
 	);
 }
 
-- 
2.32.0

[PATCH 2/2] x86/mce/amd: Fix memory leak when `threshold_create_bank()` fails

[Ammar Faizi]

@bp is a local variable, calling mce_threshold_remove_device() when
threshold_create_bank() fails will not free the @bp. Note that
mce_threshold_remove_device() frees the @bp only if it's already
stored in the @threshold_banks per-CPU variable.

At that point, the @threshold_banks per-CPU variable is still NULL,
so the mce_threshold_remove_device() will just be a no-op and the
@bp is leaked.

Fix this by calling kfree() and early returning when we fail.

This bug is introduced by commit 6458de97fc15530b544 ("x86/mce/amd:
Straighten CPU hotplug path") [1].

Link: https://lore.kernel.org/all/20200403161943.1458-6-bp@alien8.de [1]

Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Fixes: 6458de97fc15530b54477c4e2b70af653e8ac3d9 ("x86/mce/amd: Straighten CPU hotplug path")
Cc: stable@vger.kernel.org # v5.8+
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 arch/x86/kernel/cpu/mce/amd.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
index 9f4b508886dd..75d019dfe8d6 100644
--- a/arch/x86/kernel/cpu/mce/amd.c
+++ b/arch/x86/kernel/cpu/mce/amd.c
@@ -1350,15 +1350,14 @@ int mce_threshold_create_device(unsigned int cpu)
 		if (!(this_cpu_read(bank_map) & (1 << bank)))
 			continue;
 		err = threshold_create_bank(bp, cpu, bank);
-		if (err)
-			goto out_err;
+		if (err) {
+			kfree(bp);
+			return err;
+		}
 	}
 	this_cpu_write(threshold_banks, bp);
 
 	if (thresholding_irq_en)
 		mce_threshold_vector = amd_threshold_interrupt;
 	return 0;
-out_err:
-	mce_threshold_remove_device(cpu);
-	return err;
 }
-- 
2.32.0

Re: [PATCH 0/2] Two x86 fixes

[Ammar Faizi]

On 3/1/22 2:23 PM, Ammar Faizi wrote:
> [PATCH 1/2] x86/delay: Fix the wrong asm constraint in `delay_loop()`
> 
> @bp is a local variable, calling mce_threshold_remove_device() when
> threshold_create_bank() fails will not free the @bp. Note that
> mce_threshold_remove_device() frees the @bp only if it's already
> stored in the @threshold_banks per-CPU variable.
> 
> At that point, the @threshold_banks per-CPU variable is still NULL,
> so the mce_threshold_remove_device() will just be a no-op and the
> @bp is leaked.
> 
> Fix this by calling kfree() and early returning when we fail.
> 
> This bug is introduced by commit 6458de97fc15530b544 ("x86/mce/amd:
> Straighten CPU hotplug path") [1].
> 
> Link: https://lore.kernel.org/all/20200403161943.1458-6-bp@alien8.de [1]

Uhh... Wrong cover letter... Sorry... Re-sending now...

-- 
Ammar Faizi