powerpc/44x: Implement Kernel Userspace Exec Protection (KUEP)

Powerpc 44x has two bits for exec protection in TLBs: one
for user (UX) and one for superviser (SX).

Clear SX on user pages in TLB miss handlers to provide KUEP.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/169310e08152aa1d96c979770291d165ec6896ae.1622616032.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/include/asm/nohash/32/mmu-44x.h b/arch/powerpc/include/asm/nohash/32/mmu-44x.h
index 2d92a39..43ceca1 100644 (file)
--- a/arch/powerpc/include/asm/nohash/32/mmu-44x.h
+++ b/arch/powerpc/include/asm/nohash/32/mmu-44x.h
@@ -113,6 +113,7 @@ typedef struct {
 
 /* patch sites */
 extern s32 patch__tlb_44x_hwater_D, patch__tlb_44x_hwater_I;
+extern s32 patch__tlb_44x_kuep, patch__tlb_47x_kuep;
 
 #endif /* !__ASSEMBLY__ */
 

diff --git a/arch/powerpc/kernel/head_44x.S b/arch/powerpc/kernel/head_44x.S
index 5c106ac..2cfb496 100644 (file)
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S
@@ -532,6 +532,10 @@ finish_tlb_load_44x:
        andi.   r10,r12,_PAGE_USER              /* User page ? */
        beq     1f                              /* nope, leave U bits empty */
        rlwimi  r11,r11,3,26,28                 /* yes, copy S bits to U */
+#ifdef CONFIG_PPC_KUEP
+0:     rlwinm  r11,r11,0,~PPC44x_TLB_SX        /* Clear SX if User page */
+       patch_site 0b, patch__tlb_44x_kuep
+#endif
 1:     tlbwe   r11,r13,PPC44x_TLB_ATTRIB       /* Write ATTRIB */
 
        /* Done...restore registers and get out of here.
@@ -743,6 +747,10 @@ finish_tlb_load_47x:
        andi.   r10,r12,_PAGE_USER              /* User page ? */
        beq     1f                              /* nope, leave U bits empty */
        rlwimi  r11,r11,3,26,28                 /* yes, copy S bits to U */
+#ifdef CONFIG_PPC_KUEP
+0:     rlwinm  r11,r11,0,~PPC47x_TLB2_SX       /* Clear SX if User page */
+       patch_site 0b, patch__tlb_47x_kuep
+#endif
 1:     tlbwe   r11,r13,2
 
        /* Done...restore registers and get out of here.

diff --git a/arch/powerpc/mm/nohash/44x.c b/arch/powerpc/mm/nohash/44x.c
index 3d6ae7c..7da6d1e 100644 (file)
--- a/arch/powerpc/mm/nohash/44x.c
+++ b/arch/powerpc/mm/nohash/44x.c
@@ -239,3 +239,16 @@ void __init mmu_init_secondary(int cpu)
        }
 }
 #endif /* CONFIG_SMP */
+
+#ifdef CONFIG_PPC_KUEP
+void __init setup_kuep(bool disabled)
+{
+       if (disabled)
+               patch_instruction_site(&patch__tlb_44x_kuep, ppc_inst(PPC_RAW_NOP()));
+       else
+               pr_info("Activating Kernel Userspace Execution Prevention\n");
+
+       if (IS_ENABLED(CONFIG_PPC_47x) && disabled)
+               patch_instruction_site(&patch__tlb_47x_kuep, ppc_inst(PPC_RAW_NOP()));
+}
+#endif

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index dc7c46f..d4acba7 100644 (file)
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -61,6 +61,7 @@ config 44x
        select 4xx_SOC
        select HAVE_PCI
        select PHYS_64BIT
+       select PPC_HAVE_KUEP
 
 endchoice