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Mon, 22 Jan 2024 17:12:40 -0800 (PST) Received: from www.outflux.net ([198.0.35.241]) by smtp.gmail.com with ESMTPSA id t10-20020a170902bc4a00b001d714a1530bsm6628583plz.176.2024.01.22.17.12.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Jan 2024 17:12:40 -0800 (PST) From: Kees Cook To: Russell King Cc: Kees Cook , Mark Brown , Ard Biesheuvel , Wang Kefeng , Andrew Morton , Ben Hutchings , linux-arm-kernel@lists.infradead.org, "Russell King (Oracle)" , Hugh Dickins , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH] ARM: fault: Implement copy_from_kernel_nofault_allowed() Date: Mon, 22 Jan 2024 17:12:38 -0800 Message-Id: <20240123011238.work.301-kees@kernel.org> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1287; i=keescook@chromium.org; h=from:subject:message-id; bh=JA+WiZ5whi3MvySX6MkJgvqaUceqzu/DBmYXunBrTeM=; 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charset="utf-8" Under PAN emulation when dumping backtraces from things like the LKDTM EXEC_USERSPACE test[1], a double fault (which would hang a CPU) would happen because of dump_instr() attempting to read a userspace address. Make sure copy_from_kernel_nofault() does not attempt this any more. Reported-by: Mark Brown Link: https://lore.kernel.org/all/202401181125.D48DCB4C@keescook/ [1] Suggested-by: "Russell King (Oracle)" Cc: Russell King Cc: Ard Biesheuvel Cc: Wang Kefeng Cc: Andrew Morton Cc: Ben Hutchings Cc: linux-arm-kernel@lists.infradead.org Signed-off-by: Kees Cook Reviewed-by: Ard Biesheuvel Tested-by: Mark Brown --- arch/arm/mm/fault.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c index e804432e905e..bc5b959b6f90 100644 --- a/arch/arm/mm/fault.c +++ b/arch/arm/mm/fault.c @@ -25,6 +25,13 @@ =20 #include "fault.h" =20 +bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) +{ + unsigned long addr =3D (unsigned long)unsafe_src; + + return addr >=3D TASK_SIZE && ULONG_MAX - addr >=3D size; +} + #ifdef CONFIG_MMU =20 /* --=20 2.34.1