linux-kernel - Re: [PATCH v16 4/5] random: introduce generic vDSO getrandom() implementation

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Message-ID: <173853ee-348d-4f76-bc50-c5727d76b3c9@infradead.org>
Date: Fri, 31 May 2024 12:12:23 -0700
From: Randy Dunlap <rdunlap@...radead.org>
To: "Jason A. Donenfeld" <Jason@...c4.com>, linux-kernel@...r.kernel.org,
 patches@...ts.linux.dev, tglx@...utronix.de
Cc: linux-crypto@...r.kernel.org, linux-api@...r.kernel.org, x86@...nel.org,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Adhemerval Zanella Netto <adhemerval.zanella@...aro.org>,
 Carlos O'Donell <carlos@...hat.com>, Florian Weimer <fweimer@...hat.com>,
 Arnd Bergmann <arnd@...db.de>, Jann Horn <jannh@...gle.com>,
 Christian Brauner <brauner@...nel.org>,
 David Hildenbrand <dhildenb@...hat.com>
Subject: Re: [PATCH v16 4/5] random: introduce generic vDSO getrandom()
 implementation

On 5/28/24 5:19 AM, Jason A. Donenfeld wrote:
> +/**
> + * type vdso_kernel_ulong - unsigned long type that matches kernel's unsigned long

s/type/typedef/ (for first "type" only)

> + *
> + * Data shared between userspace and the kernel must operate the same way in both 64-bit code and in
> + * 32-bit compat code, over the same potentially 64-bit kernel. This type represents the size of an
> + * unsigned long as used by kernel code. This isn't necessarily the same as an unsigned long as used
> + * by userspace, however.
> + *
> + *                 +-------------------+-------------------+------------------+-------------------+
> + *                 | 32-bit userspace  | 32-bit userspace  | 64-bit userspace | 64-bit userspace  |
> + *                 | unsigned long     | vdso_kernel_ulong | unsigned long    | vdso_kernel_ulong |
> + * +---------------+-------------------+-------------------+------------------+-------------------+
> + * | 32-bit kernel | ✓ same size       | ✓ same size       |
> + * | unsigned long |                   |                   |
> + * +---------------+-------------------+-------------------+------------------+-------------------+
> + * | 64-bit kernel | ✘ different size! | ✓ same size       | ✓ same size      | ✓ same size       |
> + * | unsigned long |                   |                   |                  |                   |
> + * +---------------+-------------------+-------------------+------------------+-------------------+
> + */
> +#ifdef CONFIG_64BIT
> +typedef u64 vdso_kernel_ulong;
> +#else
> +typedef u32 vdso_kernel_ulong;
> +#endif

-- 
#Randy
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