Message-ID: <0ec52e49-3996-48e2-a16b-5d7eb0a4c8a6@linux.intel.com>
Date: Mon, 12 May 2025 16:31:23 +0800
From: Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Bernhard Kaindl <bk@...e.de>,
 Andi Kleen <ak@...ux.intel.com>, Li Fei <fei1.li@...el.com>,
 stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/mtrr: Check if fixed-range MTRR exists in
 mtrr_save_fixed_ranges()

On 2025-05-10 01:32, Borislav Petkov wrote:
> On Fri, May 09, 2025 at 05:06:33PM +0000, Jiaqing Zhao wrote:
>> When suspending, save_processor_state() calls mtrr_save_fixed_ranges()
>> to save fixed-range MTRRs. On platforms without fixed-range MTRRs,
>> accessing these MSRs will trigger unchecked MSR access error. Make
>> sure fixed-range MTRRs are supported before access to prevent such
>> error.
>>
>> Since mtrr_state.have_fixed is only set when MTRRs are present and
>> enabled, checking the CPU feature flag in mtrr_save_fixed_ranges()
>> is unnecessary.
>>
>> Fixes: 3ebad5905609 ("[PATCH] x86: Save and restore the fixed-range MTRRs of the BSP when suspending")
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>
> 
> Next question: this is CC:stable, meaning it'll go to Linus now.
> 
> What exactly is it fixing?
> 
> Because the patch in Fixes: is from 2007. :-\

Hi, Boris

This fixes unchecked MSR access error on platform without fixed-range
MTRRs when doing ACPI S3 suspend. IMHO, though it is handled and won't
panic kernel, it is worth getting fixed, and it matches the stable rule
that

"It fixes a problem like an oops, a hang, data corruption, a real
security issue, a hardware quirk, a build error (but not for things
marked CONFIG_BROKEN), or some “oh, that’s not good” issue."

Kernel log is attached below.

Thanks,
Jiaqing

[ 173.115706] ACPI: PM: Saving platform NVS memory
[ 173.115818] Disabling non-boot CPUs ...
[ 173.126530] unchecked MSR access error: RDMSR from 0x250 at rIP: 0xffffffffa90a15ff (get_fixed_ranges+0x)
[ 173.126749] Call Trace:
[ 173.126806] <TASK>
[ 173.126858] ? show_stack_regs+0x23/0x30
[ 173.126946] ? fixup_exception+0x5a4/0x610
[ 173.127037] ? printk_get_next_message+0x105/0x350
[ 173.127141] ? gp_try_fixup_and_notify+0x37/0x100
[ 173.127244] ? exc_general_protection+0xe1/0x1f0
[ 173.127346] ? asm_exc_general_protection+0x27/0x30
[ 173.127452] ? __cfi_x86_acpi_suspend_lowlevel+0x10/0x10
[ 173.127567] ? get_fixed_ranges+0x5f/0x390
[ 173.127657] mtrr_save_fixed_ranges+0x1b/0x40
[ 173.127753] save_processor_state+0x111/0x220
[ 173.127849] do_suspend_lowlevel+0xf/0xb70
[ 173.127939] x86_acpi_suspend_lowlevel+0x14c/0x180
[ 173.128042] acpi_suspend_enter+0x17e/0x1e0
[ 173.128133] suspend_devices_and_enter+0x62d/0x950
[ 173.128236] pm_suspend+0x2cf/0x4c0
[ 173.128314] state_store+0x109/0x130
[ 173.128393] kobj_attr_store+0x1e/0x40
[ 173.128477] sysfs_kf_write+0x45/0x60
[ 173.128559] kernfs_fop_write_iter+0x113/0x1a0
[ 173.128698] vfs_write+0x38a/0x470
[ 173.128775] ksys_write+0x87/0x100
[ 173.128851] __x64_sys_write+0x1b/0x30
[ 173.128932] x64_sys_call+0x17f1/0x25e0
[ 173.129017] do_syscall_64+0x74/0x120
[ 173.129098] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 173.129206] RIP: 0033:0x7d6a19d82687
[ 173.129288] Code: 00 00 00 b8 00 00 00 00 0f 05 48 3d 01 f0 ff ff 72 09 f7 d8 89 c7 e8 e8 fa ff ff c3 0f0
[ 173.129661] RSP: 002b:00007d66c7a7f668 EFLAGS: 00000213 ORIG_RAX: 0000000000000001
[ 173.129819] RAX: ffffffffffffffda RBX: 00007d68a8858450 RCX: 00007d6a19d82687
[ 173.129967] RDX: 0000000000000003 RSI: 00007d680881a2a0 RDI: 00000000000000a8
[ 173.130115] RBP: 00007d66c7a7f6e0 R08: ffffffffffffffff R09: 0000000000000000
[ 173.130262] R10: 0000000000020000 R11: 0000000000000213 R12: 0000000000000000
[ 173.130410] R13: 0000000070ec9fb8 R14: 00000000000000a8 R15: 00007d66c7a7f75c
[ 173.130559] </TASK>

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