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Peter Anvin" , Tom Lendacky , Pankaj Gupta , linux-kernel@vger.kernel.org Subject: [PATCH 1/1] x86/sev: Fix potential sign extension in amd_enc_status_change_finish() Date: Thu, 23 Apr 2026 10:10:33 +0800 Message-ID: <20260423021033.147975-1-east.moutain.yang@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit When npages (int) is left-shifted by PAGE_SHIFT to calculate the size in bytes, the operation is performed on a signed integer. If npages is large enough, this can cause: 1. Signed integer overflow (undefined behavior per C standard) 2. Sign extension when the result is promoted to unsigned long for the enc_dec_hypercall() parameter Cast npages to unsigned long before the shift to ensure: - The shift operation uses unsigned arithmetic - No sign extension occurs during parameter promotion - Correct size calculation for large page counts (>2^19 pages on 32-bit) This is a defensive fix; in practice, npages values are typically small, but the cast ensures correctness for edge cases and silences potential compiler warnings with -Wshift-overflow or -Wsign-conversion. Fixes: ac3f9c9f1b37 (x86/sev: Make enc_dec_hypercall() accept a size instead of npages) Signed-off-by: YangWencheng --- arch/x86/mm/mem_encrypt_amd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c index 2f8c32173972..8134fb731a21 100644 --- a/arch/x86/mm/mem_encrypt_amd.c +++ b/arch/x86/mm/mem_encrypt_amd.c @@ -306,7 +306,7 @@ static int amd_enc_status_change_finish(unsigned long vaddr, int npages, bool en snp_set_memory_private(vaddr, npages); if (!cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) - enc_dec_hypercall(vaddr, npages << PAGE_SHIFT, enc); + enc_dec_hypercall(vaddr, (unsigned long)npages << PAGE_SHIFT, enc); return 0; } -- 2.43.0