armv7: Add Position Independent Execution support

A U-Boot image could be loaded and executed at a different
location than it was linked at.

For example, Aspeed takes a stable release version of U-Boot image
as the golden one for recovery purposes. When the primary storage
such as flash is corrupted, the golden image would be loaded to any
SRAM/DRAM address on demands through ethernet/UART/etc and run for
rescue.

To deal with this condition, the PIE is needed as there is only one
signed, golden image, which could be however executed at different
places.

This patch adds the PIE support for ARMv7 platform.

Signed-off-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 31ae2950ee88b27304a59c3c98a442b22f9e81a0..50efb5e2e2fbe0ad9601688ab309edce2c51c8cd 100644 (file)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -11,7 +11,7 @@ config ARM64
 
 config POSITION_INDEPENDENT
        bool "Generate position-independent pre-relocation code"
-       depends on ARM64
+       depends on ARM64 || CPU_V7A
        help
          U-Boot expects to be linked to a specific hard-coded address, and to
          be loaded to and run from that address. This option lifts that

diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
index 87329d26e104a96c98ae7bbf22dbc4b9d3cc1614..698e15b8e184da24ff61ba82862086521ade16c0 100644 (file)
--- a/arch/arm/cpu/armv7/start.S
+++ b/arch/arm/cpu/armv7/start.S
@@ -39,6 +39,42 @@ reset:
        /* Allow the board to save important registers */
        b       save_boot_params
 save_boot_params_ret:
+#ifdef CONFIG_POSITION_INDEPENDENT
+       /*
+        * Fix .rela.dyn relocations. This allows U-Boot to loaded to and
+        * executed at a different address than it was linked at.
+        */
+pie_fixup:
+       adr     r0, reset       /* r0 <- Runtime value of reset label */
+       ldr     r1, =reset      /* r1 <- Linked value of reset label */
+       subs    r4, r0, r1      /* r4 <- Runtime-vs-link offset */
+       beq     pie_fixup_done
+
+       adr     r0, pie_fixup
+       ldr     r1, _rel_dyn_start_ofs
+       add     r2, r0, r1      /* r2 <- Runtime &__rel_dyn_start */
+       ldr     r1, _rel_dyn_end_ofs
+       add     r3, r0, r1      /* r3 <- Runtime &__rel_dyn_end */
+
+pie_fix_loop:
+       ldr     r0, [r2]        /* r0 <- Link location */
+       ldr     r1, [r2, #4]    /* r1 <- fixup */
+       cmp     r1, #23         /* relative fixup? */
+       bne     pie_skip_reloc
+
+       /* relative fix: increase location by offset */
+       add     r0, r4
+       ldr     r1, [r0]
+       add     r1, r4
+       str     r1, [r0]
+       str     r0, [r2]
+       add     r2, #8
+pie_skip_reloc:
+       cmp     r2, r3
+       blo     pie_fix_loop
+pie_fixup_done:
+#endif
+
 #ifdef CONFIG_ARMV7_LPAE
 /*
  * check for Hypervisor support
@@ -340,3 +376,10 @@ ENTRY(cpu_init_crit)
        b       lowlevel_init           @ go setup pll,mux,memory
 ENDPROC(cpu_init_crit)
 #endif
+
+#if CONFIG_POSITION_INDEPENDENT
+_rel_dyn_start_ofs:
+       .word   __rel_dyn_start - pie_fixup
+_rel_dyn_end_ofs:
+       .word   __rel_dyn_end - pie_fixup
+#endif

diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
index 46b6be21a8df8a3acd89568c319f8220b8f80428..956d258c9da476cd10545dac70a45cbe3df8407b 100644 (file)
--- a/arch/arm/lib/crt0.S
+++ b/arch/arm/lib/crt0.S
@@ -130,6 +130,14 @@ ENTRY(_main)
        ldr     r9, [r9, #GD_NEW_GD]            /* r9 <- gd->new_gd */
 
        adr     lr, here
+#if defined(CONFIG_POSITION_INDEPENDENT)
+       adr     r0, _main
+       ldr     r1, _start_ofs
+       add     r0, r1
+       ldr     r1, =CONFIG_SYS_TEXT_BASE
+       sub     r1, r0
+       add     lr, r1
+#endif
        ldr     r0, [r9, #GD_RELOC_OFF]         /* r0 = gd->reloc_off */
        add     lr, lr, r0
 #if defined(CONFIG_CPU_V7M)
@@ -180,3 +188,6 @@ here:
 #endif
 
 ENDPROC(_main)
+
+_start_ofs:
+       .word   _start - _main

diff --git a/arch/arm/lib/relocate.S b/arch/arm/lib/relocate.S
index e5f7267be193e09db2db3e7b32ed7a1b93c2f09b..14b7f61c1a4bb4c5b222f1be0b1252f1ab4bdd85 100644 (file)
--- a/arch/arm/lib/relocate.S
+++ b/arch/arm/lib/relocate.S
@@ -78,22 +78,28 @@ ENDPROC(relocate_vectors)
  */
 
 ENTRY(relocate_code)
-       ldr     r1, =__image_copy_start /* r1 <- SRC &__image_copy_start */
-       subs    r4, r0, r1              /* r4 <- relocation offset */
-       beq     relocate_done           /* skip relocation */
-       ldr     r2, =__image_copy_end   /* r2 <- SRC &__image_copy_end */
-
+       adr     r3, relocate_code
+       ldr     r1, _image_copy_start_ofs
+       add     r1, r3                  /* r1 <- Run &__image_copy_start */
+       subs    r4, r0, r1              /* r4 <- Run to copy offset      */
+       beq     relocate_done           /* skip relocation               */
+       ldr     r1, _image_copy_start_ofs
+       add     r1, r3                  /* r1 <- Run &__image_copy_start */
+       ldr     r2, _image_copy_end_ofs
+       add     r2, r3                  /* r2 <- Run &__image_copy_end   */
 copy_loop:
-       ldmia   r1!, {r10-r11}          /* copy from source address [r1]    */
-       stmia   r0!, {r10-r11}          /* copy to   target address [r0]    */
-       cmp     r1, r2                  /* until source end address [r2]    */
+       ldmia   r1!, {r10-r11}          /* copy from source address [r1] */
+       stmia   r0!, {r10-r11}          /* copy to   target address [r0] */
+       cmp     r1, r2                  /* until source end address [r2] */
        blo     copy_loop
 
        /*
         * fix .rel.dyn relocations
         */
-       ldr     r2, =__rel_dyn_start    /* r2 <- SRC &__rel_dyn_start */
-       ldr     r3, =__rel_dyn_end      /* r3 <- SRC &__rel_dyn_end */
+       ldr     r1, _rel_dyn_start_ofs
+       add     r2, r1, r3              /* r2 <- Run &__rel_dyn_start */
+       ldr     r1, _rel_dyn_end_ofs
+       add     r3, r1, r3              /* r3 <- Run &__rel_dyn_end */
 fixloop:
        ldmia   r2!, {r0-r1}            /* (r0,r1) <- (SRC location,fixup) */
        and     r1, r1, #0xff
@@ -129,3 +135,12 @@ relocate_done:
 #endif
 
 ENDPROC(relocate_code)
+
+_image_copy_start_ofs:
+       .word   __image_copy_start - relocate_code
+_image_copy_end_ofs:
+       .word   __image_copy_end - relocate_code
+_rel_dyn_start_ofs:
+       .word   __rel_dyn_start - relocate_code
+_rel_dyn_end_ofs:
+       .word   __rel_dyn_end - relocate_code