linux-kernel - Re: [PATCH] x86/ioremap: Fix off-by-one in e820 check in memremap_should_map

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Message-ID: <05f00515-1400-2f39-0bdb-b963994bf882@amd.com>
Date: Fri, 18 Apr 2025 09:43:43 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Dmytro Maluka <dmaluka@...omium.org>,
 Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>,
 "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
 "H. Peter Anvin" <hpa@...or.com>,
 "open list:X86 MM" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/ioremap: Fix off-by-one in e820 check in
 memremap_should_map_decrypted()

On 4/18/25 08:59, Dmytro Maluka wrote:
> The end address in e820__get_entry_type() is exclusive, not inclusive.
> 
> Note: untested, bug found by code inspection.
> 
> Signed-off-by: Dmytro Maluka <dmaluka@...omium.org>
> ---
>  arch/x86/mm/ioremap.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index 331e101bf801..a44800a6196e 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -578,7 +578,7 @@ static bool memremap_should_map_decrypted(resource_size_t phys_addr,
>  	}
>  
>  	/* Check if the address is outside kernel usable area */
> -	switch (e820__get_entry_type(phys_addr, phys_addr + size - 1)) {
> +	switch (e820__get_entry_type(phys_addr, phys_addr + size)) {

I don't think removing the " - 1" is correct. For example, if you are
mapping a page-aligned value for page-size (4K), then not subtracting 1
will place you on the next page, which is incorrect, because you are not
mapping that page.

Thanks,
Tom

>  	case E820_TYPE_RESERVED:
>  	case E820_TYPE_ACPI:
>  	case E820_TYPE_NVS: