powerpc/603: Fix protection of user pages mapped with PROT_NONE
stable inclusion from stable-5.10.24 commit aa1258d91455a75474d0541f746537c9bb0484c3 bugzilla: 51348 -------------------------------- commit c119565a upstream. On book3s/32, page protection is defined by the PP bits in the PTE which provide the following protection depending on the access keys defined in the matching segment register: - PP 00 means RW with key 0 and N/A with key 1. - PP 01 means RW with key 0 and RO with key 1. - PP 10 means RW with both key 0 and key 1. - PP 11 means RO with both key 0 and key 1. Since the implementation of kernel userspace access protection, PP bits have been set as follows: - PP00 for pages without _PAGE_USER - PP01 for pages with _PAGE_USER and _PAGE_RW - PP11 for pages with _PAGE_USER and without _PAGE_RW For kernelspace segments, kernel accesses are performed with key 0 and user accesses are performed with key 1. As PP00 is used for non _PAGE_USER pages, user can't access kernel pages not flagged _PAGE_USER while kernel can. For userspace segments, both kernel and user accesses are performed with key 0, therefore pages not flagged _PAGE_USER are still accessible to the user. This shouldn't be an issue, because userspace is expected to be accessible to the user. But unlike most other architectures, powerpc implements PROT_NONE protection by removing _PAGE_USER flag instead of flagging the page as not valid. This means that pages in userspace that are not flagged _PAGE_USER shall remain inaccessible. To get the expected behaviour, just mimic other architectures in the TLB miss handler by checking _PAGE_USER permission on userspace accesses as if it was the _PAGE_PRESENT bit. Note that this problem only is only for 603 cores. The 604+ have an hash table, and hash_page() function already implement the verification of _PAGE_USER permission on userspace pages. Fixes: f342adca ("powerpc/32s: Prepare Kernel Userspace Access Protection") Cc: stable@vger.kernel.org # v5.2+ Reported-by: NChristoph Plattner <christoph.plattner@thalesgroup.com> Signed-off-by: NChristophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/4a0c6e3bb8f0c162457bf54d9bc6fd8d7b55129f.1612160907.git.christophe.leroy@csgroup.euSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: NChen Jun <chenjun102@huawei.com> Acked-by: N Weilong Chen <chenweilong@huawei.com> Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>
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