[Buildroot] [PATCH] uclibc: powerpc: fix PIE/PIC builds with secureplt enabled by default
Arnout Vandecappelle
arnout at mind.be
Tue Jun 1 19:53:10 UTC 2021
On 01/06/2021 21:16, Romain Naour wrote:
> Apply the fix provided by Yann Sionneau when secureplt is enabled
> by default by gcc compiler along with PIE/PIC options.
>
> "For the secure PLT to work in PIC, the r30 register needs to point to the GOT"
>
> Fixes:
> [qemu_ppc_e500mc_defconfig] https://gitlab.com/buildroot.org/buildroot/-/jobs/1255661606
> [qemu_ppc_g3beige_defconfig] https://gitlab.com/buildroot.org/buildroot/-/jobs/1255661607
> [qemu_ppc_mac99_defconfig] https://gitlab.com/buildroot.org/buildroot/-/jobs/1255661609
>
> Signed-off-by: Romain Naour <romain.naour at gmail.com>
> Cc: Yann Sionneau <yann at sionneau.net>
Applied to master, thanks.
Perhaps I should have waited a few days for feedback from the uclibc-ng mailing
list... Oh well.
Regards,
Arnout
> ---
> ...PIC-builds-with-newer-gcc-binutils-w.patch | 91 +++++++++++++++++++
> 1 file changed, 91 insertions(+)
> create mode 100644 package/uclibc/0001-powerpc-fix-PIE-PIC-builds-with-newer-gcc-binutils-w.patch
>
> diff --git a/package/uclibc/0001-powerpc-fix-PIE-PIC-builds-with-newer-gcc-binutils-w.patch b/package/uclibc/0001-powerpc-fix-PIE-PIC-builds-with-newer-gcc-binutils-w.patch
> new file mode 100644
> index 0000000000..040699df83
> --- /dev/null
> +++ b/package/uclibc/0001-powerpc-fix-PIE-PIC-builds-with-newer-gcc-binutils-w.patch
> @@ -0,0 +1,91 @@
> +From 6c95eccff5eb43c8c3ad865d3b1316b7952cc58e Mon Sep 17 00:00:00 2001
> +From: Yann Sionneau <yann at sionneau.net>
> +Date: Fri, 28 May 2021 08:59:58 +0200
> +Subject: [PATCH] powerpc: fix PIE/PIC builds with newer gcc/binutils which use
> + secureplt by default
> +
> +This patch fixes segfault of all user space processes (including init, which caused a panic) on recent buildroot powerpc32 builds.
> +
> +The issue has been reported by Romain Naour in this thread: https://mailman.uclibc-ng.org/pipermail/devel/2021-May/002068.html
> +
> +Recent buildroot toolchain enables secure PLT in powerpc gcc.
> +The latter will then supply -msecure-plt to gas invocations by default.
> +Recent buildroot also enables PIE by default.
> +
> +For the secure PLT to work in PIC, the r30 register needs to point to the GOT.
> +Old "bss plt" was just a one-instruction-wide PLT slot, pointed-to by a R_PPC_JMP_SLOT relocation, which was written on-the-fly to contain a branch instruction to the correct address. It therefore had to stay writable+executable, which you generally want to avoid for security reasons.
> +New secure PLT only contains read-only code which loads the branch address from the writable GOT.
> +
> +Note: secure PLT without PIC does not need r30 to be set. Because offset between plt stub code and got is known at link-time. In this case the PLT entry looks like:
> +1009b3e0 <__uClibc_main at plt>:
> +1009b3e0: 3d 60 10 0e lis r11,4110
> +1009b3e4: 81 6b 03 74 lwz r11,884(r11)
> +1009b3e8: 7d 69 03 a6 mtctr r11
> +1009b3ec: 4e 80 04 20 bctr
> +
> +Whereas secure PLT with PIC - offset between plt and got is unknown at link-time - looks like this:
> +000af800 <00000000.plt_pic32.__uClibc_main>:
> + af800: 81 7e 03 80 lwz r11,896(r30)
> + af804: 7d 69 03 a6 mtctr r11
> + af808: 4e 80 04 20 bctr
> + af80c: 60 00 00 00 nop
> +
> +Upstream status: Pending:
> +https://mailman.uclibc-ng.org/pipermail/devel/2021-May/002091.html
> +
> +Signed-off-by: Yann Sionneau <yann at sionneau.net>
> +Signed-off-by: Romain Naour <romain.naour at gmail.com>
> +---
> + Rules.mak | 3 ++-
> + ldso/ldso/powerpc/dl-startup.h | 3 +++
> + libc/sysdeps/linux/powerpc/crt1.S | 4 ++++
> + 3 files changed, 9 insertions(+), 1 deletion(-)
> +
> +diff --git a/Rules.mak b/Rules.mak
> +index 10f88b3de..60ac59b85 100644
> +--- a/Rules.mak
> ++++ b/Rules.mak
> +@@ -477,9 +477,10 @@ ifeq ($(TARGET_ARCH),powerpc)
> + PICFLAG:=-fpic
> + PIEFLAG_NAME:=-fpie
> + PPC_HAS_REL16:=$(shell printf "\t.text\n\taddis 11,30,_GLOBAL_OFFSET_TABLE_-. at ha\n" | $(CC) -c -x assembler -o /dev/null - 2> /dev/null && echo -n y || echo -n n)
> ++ PPC_HAS_SECUREPLT:=$(shell $(CC) --verbose 2>&1 | grep -- --enable-secureplt > /dev/null && echo -n y || echo -n n)
> ++ CPU_CFLAGS-$(PPC_HAS_SECUREPLT) += -DPPC_HAS_SECUREPLT
> + CPU_CFLAGS-$(PPC_HAS_REL16)+= -DHAVE_ASM_PPC_REL16
> + CPU_CFLAGS-$(CONFIG_E500) += "-D__NO_MATH_INLINES"
> +-
> + endif
> +
> + ifeq ($(TARGET_ARCH),bfin)
> +diff --git a/ldso/ldso/powerpc/dl-startup.h b/ldso/ldso/powerpc/dl-startup.h
> +index 8b2a517e2..7749395eb 100644
> +--- a/ldso/ldso/powerpc/dl-startup.h
> ++++ b/ldso/ldso/powerpc/dl-startup.h
> +@@ -25,6 +25,9 @@ __asm__(
> + #else
> + " bl _GLOBAL_OFFSET_TABLE_-4 at local\n" /* Put our GOT pointer in r31, */
> + " mflr 31\n"
> ++#endif
> ++#ifdef PPC_HAS_SECUREPLT
> ++ " mr 30,31\n"
> + #endif
> + " addi 1,1,16\n" /* Restore SP */
> + " lwz 7,_dl_skip_args at got(31)\n" /* load EA of _dl_skip_args */
> +diff --git a/libc/sysdeps/linux/powerpc/crt1.S b/libc/sysdeps/linux/powerpc/crt1.S
> +index 27bfc5a5a..3f5d056c0 100644
> +--- a/libc/sysdeps/linux/powerpc/crt1.S
> ++++ b/libc/sysdeps/linux/powerpc/crt1.S
> +@@ -56,6 +56,10 @@ _start:
> + # else
> + bl _GLOBAL_OFFSET_TABLE_-4 at local
> + mflr r31
> ++# endif
> ++ /* in PIC/PIE, plt stubs need r30 to point to the GOT if using secure-plt */
> ++# ifdef PPC_HAS_SECUREPLT
> ++ mr 30,31
> + # endif
> + #endif
> + /* Set up the small data pointer in r13. */
> +--
> +2.31.1
> +
>
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