powerpc/32s: Implement Kernel Userspace Execution Prevention.

To implement Kernel Userspace Execution Prevention, this patch
sets NX bit on all user segments on kernel entry and clears NX bit
on all user segments on kernel exit.

Note that powerpc 601 doesn't have the NX bit, so KUEP will not
work on it. A warning is displayed at startup.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
new file mode 100644 (file)
index 0000000..5f97c74
--- /dev/null
+++ b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_POWERPC_BOOK3S_32_KUP_H
+#define _ASM_POWERPC_BOOK3S_32_KUP_H
+
+#include <asm/book3s/32/mmu-hash.h>
+
+#ifdef __ASSEMBLY__
+
+.macro kuep_update_sr  gpr1, gpr2              /* NEVER use r0 as gpr2 due to addis */
+101:   mtsrin  \gpr1, \gpr2
+       addi    \gpr1, \gpr1, 0x111             /* next VSID */
+       rlwinm  \gpr1, \gpr1, 0, 0xf0ffffff     /* clear VSID overflow */
+       addis   \gpr2, \gpr2, 0x1000            /* address of next segment */
+       bdnz    101b
+       isync
+.endm
+
+.macro kuep_lock       gpr1, gpr2
+#ifdef CONFIG_PPC_KUEP
+       li      \gpr1, NUM_USER_SEGMENTS
+       li      \gpr2, 0
+       mtctr   \gpr1
+       mfsrin  \gpr1, \gpr2
+       oris    \gpr1, \gpr1, SR_NX@h           /* set Nx */
+       kuep_update_sr \gpr1, \gpr2
+#endif
+.endm
+
+.macro kuep_unlock     gpr1, gpr2
+#ifdef CONFIG_PPC_KUEP
+       li      \gpr1, NUM_USER_SEGMENTS
+       li      \gpr2, 0
+       mtctr   \gpr1
+       mfsrin  \gpr1, \gpr2
+       rlwinm  \gpr1, \gpr1, 0, ~SR_NX         /* Clear Nx */
+       kuep_update_sr \gpr1, \gpr2
+#endif
+.endm
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* _ASM_POWERPC_BOOK3S_32_KUP_H */

diff --git a/arch/powerpc/include/asm/book3s/32/mmu-hash.h b/arch/powerpc/include/asm/book3s/32/mmu-hash.h
index 5cb5883..8c5727a 100644 (file)
--- a/arch/powerpc/include/asm/book3s/32/mmu-hash.h
+++ b/arch/powerpc/include/asm/book3s/32/mmu-hash.h
@@ -63,6 +63,9 @@ typedef pte_t *pgtable_t;
 #define PP_RWRW 2      /* Supervisor read/write, User read/write */
 #define PP_RXRX 3      /* Supervisor read,       User read */
 
+/* Values for Segment Registers */
+#define SR_NX  0x10000000      /* No Execute */
+
 #ifndef __ASSEMBLY__
 
 /*

diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 043c800..5b5e396 100644 (file)
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -8,6 +8,9 @@
 #ifdef CONFIG_PPC_8xx
 #include <asm/nohash/32/kup-8xx.h>
 #endif
+#ifdef CONFIG_PPC_BOOK3S_32
+#include <asm/book3s/32/kup.h>
+#endif
 
 #ifdef __ASSEMBLY__
 #ifndef CONFIG_PPC_KUAP

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 1182bf6..2f3d159 100644 (file)
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -162,6 +162,9 @@ transfer_to_handler:
        andis.  r12,r12,DBCR0_IDM@h
 #endif
        ACCOUNT_CPU_USER_ENTRY(r2, r11, r12)
+#ifdef CONFIG_PPC_BOOK3S_32
+       kuep_lock r11, r12
+#endif
 #if defined(CONFIG_40x) || defined(CONFIG_BOOKE)
        beq+    3f
        /* From user and task is ptraced - load up global dbcr0 */
@@ -427,6 +430,9 @@ BEGIN_FTR_SECTION
 END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
        stwcx.  r0,0,r1                 /* to clear the reservation */
        ACCOUNT_CPU_USER_EXIT(r2, r5, r7)
+#ifdef CONFIG_PPC_BOOK3S_32
+       kuep_unlock r5, r7
+#endif
        kuap_check r2, r4
        lwz     r4,_LINK(r1)
        lwz     r5,_CCR(r1)
@@ -821,6 +827,9 @@ restore_user:
        bnel-   load_dbcr0
 #endif
        ACCOUNT_CPU_USER_EXIT(r2, r10, r11)
+#ifdef CONFIG_PPC_BOOK3S_32
+       kuep_unlock     r10, r11
+#endif
 
        b       restore
 

diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index e25b615..19b46cb 100644 (file)
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -896,14 +896,24 @@ load_up_mmu:
        tophys(r6,r6)
        lwz     r6,_SDR1@l(r6)
        mtspr   SPRN_SDR1,r6
-       li      r0,16           /* load up segment register values */
+       li      r0, NUM_USER_SEGMENTS   /* load up segment register values */
        mtctr   r0              /* for context 0 */
        lis     r3,0x2000       /* Ku = 1, VSID = 0 */
+#ifdef CONFIG_PPC_KUEP
+       oris    r3, r3, SR_NX@h /* Set Nx */
+#endif
        li      r4,0
 3:     mtsrin  r3,r4
        addi    r3,r3,0x111     /* increment VSID */
        addis   r4,r4,0x1000    /* address of next segment */
        bdnz    3b
+       li      r0, 16 - NUM_USER_SEGMENTS /* load up kernel segment registers */
+       mtctr   r0                      /* for context 0 */
+       rlwinm  r3, r3, 0, ~SR_NX       /* Nx = 0 */
+3:     mtsrin  r3, r4
+       addi    r3, r3, 0x111   /* increment VSID */
+       addis   r4, r4, 0x1000  /* address of next segment */
+       bdnz    3b
 
 /* Load the BAT registers with the values set up by MMU_init.
    MMU_init takes care of whether we're on a 601 or not. */
@@ -1007,6 +1017,9 @@ _ENTRY(switch_mmu_context)
        mulli   r3,r3,897       /* multiply context by skew factor */
        rlwinm  r3,r3,4,8,27    /* VSID = (context & 0xfffff) << 4 */
        addis   r3,r3,0x6000    /* Set Ks, Ku bits */
+#ifdef CONFIG_PPC_KUEP
+       oris    r3, r3, SR_NX@h /* Set Nx */
+#endif
        li      r0,NUM_USER_SEGMENTS
        mtctr   r0
 

diff --git a/arch/powerpc/mm/ppc_mmu_32.c b/arch/powerpc/mm/ppc_mmu_32.c
index f29d2f1..baa7567 100644 (file)
--- a/arch/powerpc/mm/ppc_mmu_32.c
+++ b/arch/powerpc/mm/ppc_mmu_32.c
@@ -394,3 +394,16 @@ void setup_initial_memory_limit(phys_addr_t first_memblock_base,
        else /* Anything else has 256M mapped */
                memblock_set_current_limit(min_t(u64, first_memblock_size, 0x10000000));
 }
+
+#ifdef CONFIG_PPC_KUEP
+void __init setup_kuep(bool disabled)
+{
+       pr_info("Activating Kernel Userspace Execution Prevention\n");
+
+       if (cpu_has_feature(CPU_FTR_601))
+               pr_warn("KUEP is not working on powerpc 601 (No NX bit in Seg Regs)\n");
+
+       if (disabled)
+               pr_warn("KUEP cannot be disabled yet on 6xx when compiled in\n");
+}
+#endif

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index ab58696..6bc0a4c 100644 (file)
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -25,6 +25,7 @@ config PPC_BOOK3S_32
        bool "512x/52xx/6xx/7xx/74xx/82xx/83xx/86xx"
        select PPC_FPU
        select PPC_HAVE_PMU_SUPPORT
+       select PPC_HAVE_KUEP
 
 config PPC_85xx
        bool "Freescale 85xx"