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[80.230.85.71]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4601f2e4b18sm62096991f8f.10.2026.06.11.00.30.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Jun 2026 00:30:18 -0700 (PDT) Date: Thu, 11 Jun 2026 03:30:14 -0400 From: "Michael S. Tsirkin" To: Herbert Xu Cc: Michael Bommarito , Olivia Mackall , linux-crypto@vger.kernel.org, Jason Wang , Kees Cook , Christian Borntraeger , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, Dan Williams , Ingo Molnar , "H. Peter Anvin" , torvalds@linux-foundation.org, alan@linux.intel.com, tglx@linutronix.de Subject: Re: [PATCH v3] hwrng: virtio: clamp device-reported used.len at copy_data() Message-ID: <20260611025916-mutt-send-email-mst@kernel.org> References: <20260531142251.2792061-1-michael.bommarito@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Jun 11, 2026 at 12:43:09PM +0800, Herbert Xu wrote: > On Sun, May 31, 2026 at 10:22:51AM -0400, Michael Bommarito wrote: > > > > + size = min_t(unsigned int, size, avail - vi->data_idx); > > + idx = array_index_nospec(vi->data_idx, sizeof(vi->data)); > > + memcpy(buf, vi->data + idx, size); > > I don't see how nospec can help here. Please enlighten me. All the "malicious device" things are confusing. Spectre things - doubly so. So if an access is speculated then CPU might speculate feeding a kernel secret into RNG. And then the speculated RNG value maybe can be also speculatively be used by some kernel code as an index to trigger a cache access, finally leaking the secret? Maybe? > Thanks, > -- > Email: Herbert Xu > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt