powerpc/book3s64/kuap: Restrict access to userspace based on userspace AMR

If an application has configured address protection such that read/write is
denied using pkey even the kernel should receive a FAULT on accessing the same.

This patch use user AMR value stored in pt_regs.amr to achieve the same.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: Sandipan Das <sandipan@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201127044424.40686-16-aneesh.kumar@linux.ibm.com

diff --git a/arch/powerpc/include/asm/book3s/64/kup.h b/arch/powerpc/include/asm/book3s/64/kup.h
index f41f6f468002911eb5d1a96e7ec4a74100355c94..4fa0760a47a46032e4bfcb442461a928c60b7a6f 100644 (file)
--- a/arch/powerpc/include/asm/book3s/64/kup.h
+++ b/arch/powerpc/include/asm/book3s/64/kup.h
@@ -314,14 +314,20 @@ bad_kuap_fault(struct pt_regs *regs, unsigned long address, bool is_write)
 static __always_inline void allow_user_access(void __user *to, const void __user *from,
                                              unsigned long size, unsigned long dir)
 {
+       unsigned long thread_amr = 0;
+
        // This is written so we can resolve to a single case at build time
        BUILD_BUG_ON(!__builtin_constant_p(dir));
+
+       if (mmu_has_feature(MMU_FTR_PKEY))
+               thread_amr = current_thread_amr();
+
        if (dir == KUAP_READ)
-               set_kuap(AMR_KUAP_BLOCK_WRITE);
+               set_kuap(thread_amr | AMR_KUAP_BLOCK_WRITE);
        else if (dir == KUAP_WRITE)
-               set_kuap(AMR_KUAP_BLOCK_READ);
+               set_kuap(thread_amr | AMR_KUAP_BLOCK_READ);
        else if (dir == KUAP_READ_WRITE)
-               set_kuap(0);
+               set_kuap(thread_amr);
        else
                BUILD_BUG();
 }