Hi,
This attempts to implement PT_LOAD p_align support for static PIE builds. I intend this to go into -next after the coming merge window so we can maximize bake time. In the past we've had regressions with both the selftests and the ELF loader. Hopefully we can shake everything out over a few months. :)
Thanks!
-Kees
Kees Cook (3): selftests/exec: Build both static and non-static load_address tests binfmt_elf: Calculate total_size earlier binfmt_elf: Honor PT_LOAD alignment for static PIE
fs/binfmt_elf.c | 94 ++++++++++++++------- tools/testing/selftests/exec/Makefile | 19 +++-- tools/testing/selftests/exec/load_address.c | 67 ++++++++++++--- 3 files changed, 130 insertions(+), 50 deletions(-)
After commit 4d1cd3b2c5c1 ("tools/testing/selftests/exec: fix link error"), the load address alignment tests tried to build statically. This was silently ignored in some cases. However, after attempting to further fix the build by switching to "-static-pie", the test started failing. This appears to be due to non-PT_INTERP ET_DYN execs ("static PIE") not doing alignment correctly, which remains unfixed[1]. See commit aeb7923733d1 ("revert "fs/binfmt_elf: use PT_LOAD p_align values for static PIE"") for more details.
Provide rules to build both static and non-static PIE binaries, improve debug reporting, and perform several test steps instead of a single all-or-nothing test. However, do not actually enable static-pie tests; alignment specification is only supported for ET_DYN with PT_INTERP ("regular PIE").
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215275 [1] Signed-off-by: Kees Cook keescook@chromium.org --- Cc: Chris Kennelly ckennelly@google.com Cc: Eric Biederman ebiederm@xmission.com Cc: Shuah Khan shuah@kernel.org Cc: Muhammad Usama Anjum usama.anjum@collabora.com Cc: John Hubbard jhubbard@nvidia.com Cc: Fangrui Song maskray@google.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Yang Yingliang yangyingliang@huawei.com Cc: linux-mm@kvack.org Cc: linux-kselftest@vger.kernel.org --- tools/testing/selftests/exec/Makefile | 19 +++--- tools/testing/selftests/exec/load_address.c | 67 +++++++++++++++++---- 2 files changed, 66 insertions(+), 20 deletions(-)
diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile index fb4472ddffd8..619cff81d796 100644 --- a/tools/testing/selftests/exec/Makefile +++ b/tools/testing/selftests/exec/Makefile @@ -3,8 +3,13 @@ CFLAGS = -Wall CFLAGS += -Wno-nonnull CFLAGS += -D_GNU_SOURCE
+ALIGNS := 0x1000 0x200000 0x1000000 +ALIGN_PIES := $(patsubst %,load_address.%,$(ALIGNS)) +ALIGN_STATIC_PIES := $(patsubst %,load_address.static.%,$(ALIGNS)) +ALIGNMENT_TESTS := $(ALIGN_PIES) + TEST_PROGS := binfmt_script.py -TEST_GEN_PROGS := execveat load_address_4096 load_address_2097152 load_address_16777216 non-regular +TEST_GEN_PROGS := execveat non-regular $(ALIGNMENT_TESTS) TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir # Makefile is a run-time dependency, since it's accessed by the execveat test TEST_FILES := Makefile @@ -28,9 +33,9 @@ $(OUTPUT)/execveat.symlink: $(OUTPUT)/execveat $(OUTPUT)/execveat.denatured: $(OUTPUT)/execveat cp $< $@ chmod -x $@ -$(OUTPUT)/load_address_4096: load_address.c - $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x1000 -pie -static $< -o $@ -$(OUTPUT)/load_address_2097152: load_address.c - $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x200000 -pie -static $< -o $@ -$(OUTPUT)/load_address_16777216: load_address.c - $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x1000000 -pie -static $< -o $@ +$(OUTPUT)/load_address.0x%: load_address.c + $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=$(lastword $(subst ., ,$@)) \ + -fPIE -pie $< -o $@ +$(OUTPUT)/load_address.static.0x%: load_address.c + $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=$(lastword $(subst ., ,$@)) \ + -fPIE -static-pie $< -o $@ diff --git a/tools/testing/selftests/exec/load_address.c b/tools/testing/selftests/exec/load_address.c index 17e3207d34ae..8257fddba8c8 100644 --- a/tools/testing/selftests/exec/load_address.c +++ b/tools/testing/selftests/exec/load_address.c @@ -5,11 +5,13 @@ #include <link.h> #include <stdio.h> #include <stdlib.h> +#include <stdbool.h> #include "../kselftest.h"
struct Statistics { unsigned long long load_address; unsigned long long alignment; + bool interp; };
int ExtractStatistics(struct dl_phdr_info *info, size_t size, void *data) @@ -26,11 +28,20 @@ int ExtractStatistics(struct dl_phdr_info *info, size_t size, void *data) stats->alignment = 0;
for (i = 0; i < info->dlpi_phnum; i++) { + unsigned long long align; + + if (info->dlpi_phdr[i].p_type == PT_INTERP) { + stats->interp = true; + continue; + } + if (info->dlpi_phdr[i].p_type != PT_LOAD) continue;
- if (info->dlpi_phdr[i].p_align > stats->alignment) - stats->alignment = info->dlpi_phdr[i].p_align; + align = info->dlpi_phdr[i].p_align; + + if (align > stats->alignment) + stats->alignment = align; }
return 1; // Terminate dl_iterate_phdr. @@ -38,27 +49,57 @@ int ExtractStatistics(struct dl_phdr_info *info, size_t size, void *data)
int main(int argc, char **argv) { - struct Statistics extracted; - unsigned long long misalign; + struct Statistics extracted = { }; + unsigned long long misalign, pow2; + bool interp_needed; + char buf[1024]; + FILE *maps; int ret;
ksft_print_header(); - ksft_set_plan(1); + ksft_set_plan(4); + + /* Dump maps file for debugging reference. */ + maps = fopen("/proc/self/maps", "r"); + if (!maps) + ksft_exit_fail_msg("FAILED: /proc/self/maps: %s\n", strerror(errno)); + while (fgets(buf, sizeof(buf), maps)) { + ksft_print_msg("%s", buf); + } + fclose(maps);
+ /* Walk the program headers. */ ret = dl_iterate_phdr(ExtractStatistics, &extracted); if (ret != 1) ksft_exit_fail_msg("FAILED: dl_iterate_phdr\n");
- if (extracted.alignment == 0) - ksft_exit_fail_msg("FAILED: No alignment found\n"); - else if (extracted.alignment & (extracted.alignment - 1)) - ksft_exit_fail_msg("FAILED: Alignment is not a power of 2\n"); + /* Report our findings. */ + ksft_print_msg("load_address=%#llx alignment=%#llx\n", + extracted.load_address, extracted.alignment); + + /* If we're named with ".static." we expect no INTERP. */ + interp_needed = strstr(argv[0], ".static.") == NULL; + + /* Were we built as expected? */ + ksft_test_result(interp_needed == extracted.interp, + "%s INTERP program header %s\n", + interp_needed ? "Wanted" : "Unwanted", + extracted.interp ? "seen" : "missing"); + + /* Did we find an alignment? */ + ksft_test_result(extracted.alignment != 0, + "Alignment%s found\n", extracted.alignment ? "" : " NOT"); + + /* Is the alignment sane? */ + pow2 = extracted.alignment & (extracted.alignment - 1); + ksft_test_result(pow2 == 0, + "Alignment is%s a power of 2: %#llx\n", + pow2 == 0 ? "" : " NOT", extracted.alignment);
+ /* Is the load address aligned? */ misalign = extracted.load_address & (extracted.alignment - 1); - if (misalign) - ksft_exit_fail_msg("FAILED: alignment = %llu, load_address = %llu\n", - extracted.alignment, extracted.load_address); + ksft_test_result(misalign == 0, "Load Address is %saligned (%#llx)\n", + misalign ? "MIS" : "", misalign);
- ksft_test_result_pass("Completed\n"); ksft_finished(); }
On 5/8/24 10:31 AM, Kees Cook wrote:
After commit 4d1cd3b2c5c1 ("tools/testing/selftests/exec: fix link error"), the load address alignment tests tried to build statically. This was silently ignored in some cases. However, after attempting to further fix the build by switching to "-static-pie", the test started failing. This appears to be due to non-PT_INTERP ET_DYN execs ("static PIE") not doing alignment correctly, which remains unfixed[1]. See commit aeb7923733d1 ("revert "fs/binfmt_elf: use PT_LOAD p_align values for static PIE"") for more details.
Provide rules to build both static and non-static PIE binaries, improve debug reporting, and perform several test steps instead of a single all-or-nothing test. However, do not actually enable static-pie tests; alignment specification is only supported for ET_DYN with PT_INTERP ("regular PIE").
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215275 [1] Signed-off-by: Kees Cook keescook@chromium.org
Cc: Chris Kennelly ckennelly@google.com Cc: Eric Biederman ebiederm@xmission.com Cc: Shuah Khan shuah@kernel.org Cc: Muhammad Usama Anjum usama.anjum@collabora.com Cc: John Hubbard jhubbard@nvidia.com Cc: Fangrui Song maskray@google.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Yang Yingliang yangyingliang@huawei.com Cc: linux-mm@kvack.org Cc: linux-kselftest@vger.kernel.org
tools/testing/selftests/exec/Makefile | 19 +++--- tools/testing/selftests/exec/load_address.c | 67 +++++++++++++++++---- 2 files changed, 66 insertions(+), 20 deletions(-)
diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile index fb4472ddffd8..619cff81d796 100644 --- a/tools/testing/selftests/exec/Makefile +++ b/tools/testing/selftests/exec/Makefile @@ -3,8 +3,13 @@ CFLAGS = -Wall CFLAGS += -Wno-nonnull CFLAGS += -D_GNU_SOURCE +ALIGNS := 0x1000 0x200000 0x1000000 +ALIGN_PIES := $(patsubst %,load_address.%,$(ALIGNS)) +ALIGN_STATIC_PIES := $(patsubst %,load_address.static.%,$(ALIGNS)) +ALIGNMENT_TESTS := $(ALIGN_PIES)
- TEST_PROGS := binfmt_script.py
-TEST_GEN_PROGS := execveat load_address_4096 load_address_2097152 load_address_16777216 non-regular +TEST_GEN_PROGS := execveat non-regular $(ALIGNMENT_TESTS) TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir # Makefile is a run-time dependency, since it's accessed by the execveat test TEST_FILES := Makefile @@ -28,9 +33,9 @@ $(OUTPUT)/execveat.symlink: $(OUTPUT)/execveat $(OUTPUT)/execveat.denatured: $(OUTPUT)/execveat cp $< $@ chmod -x $@ -$(OUTPUT)/load_address_4096: load_address.c
- $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x1000 -pie -static $< -o $@
-$(OUTPUT)/load_address_2097152: load_address.c
- $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x200000 -pie -static $< -o $@
-$(OUTPUT)/load_address_16777216: load_address.c
- $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=0x1000000 -pie -static $< -o $@
+$(OUTPUT)/load_address.0x%: load_address.c
- $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=$(lastword $(subst ., ,$@)) \
-fPIE -pie $< -o $@+$(OUTPUT)/load_address.static.0x%: load_address.c
- $(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=$(lastword $(subst ., ,$@)) \
-fPIE -static-pie $< -o $@
Hi Kees,
Didn't we learn recently, though, that -static-pie is gcc 8.1+, while the kernel's minimum gcc version is 5?
thanks,
On Wed, May 08, 2024 at 07:54:13PM -0700, John Hubbard wrote:
Didn't we learn recently, though, that -static-pie is gcc 8.1+, while the kernel's minimum gcc version is 5?
Yes, that's true. If we encounter anyone trying to build the selftests with <8.1 I think we'll have to add a compiler version test in the Makefile to exclude the static pie tests.
There's also the potential issue with arm64 builds that caused the original attempt at -static. We'll likely need an exclusion there too.
In preparation to support PT_LOAD with large p_align values on non-PT_INTERP ET_DYN executables (i.e. "static pie"), we'll need to use the total_size details earlier. Move this separately now to make the next patch more readable. As total_size and load_bias are currently calculated separately, this has no behavioral impact.
Signed-off-by: Kees Cook keescook@chromium.org --- fs/binfmt_elf.c | 52 +++++++++++++++++++++++++------------------------ 1 file changed, 27 insertions(+), 25 deletions(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 5397b552fbeb..56432e019d4e 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -1061,7 +1061,34 @@ static int load_elf_binary(struct linux_binprm *bprm) * Header for ET_DYN binaries to calculate the * randomization (load_bias) for all the LOAD * Program Headers. + */ + + /* + * Calculate the entire size of the ELF mapping + * (total_size), used for the initial mapping, + * due to load_addr_set which is set to true later + * once the initial mapping is performed. + * + * Note that this is only sensible when the LOAD + * segments are contiguous (or overlapping). If + * used for LOADs that are far apart, this would + * cause the holes between LOADs to be mapped, + * running the risk of having the mapping fail, + * as it would be larger than the ELF file itself. * + * As a result, only ET_DYN does this, since + * some ET_EXEC (e.g. ia64) may have large virtual + * memory holes between LOADs. + * + */ + total_size = total_mapping_size(elf_phdata, + elf_ex->e_phnum); + if (!total_size) { + retval = -EINVAL; + goto out_free_dentry; + } + + /* * There are effectively two types of ET_DYN * binaries: programs (i.e. PIE: ET_DYN with INTERP) * and loaders (ET_DYN without INTERP, since they @@ -1102,31 +1129,6 @@ static int load_elf_binary(struct linux_binprm *bprm) * is then page aligned. */ load_bias = ELF_PAGESTART(load_bias - vaddr); - - /* - * Calculate the entire size of the ELF mapping - * (total_size), used for the initial mapping, - * due to load_addr_set which is set to true later - * once the initial mapping is performed. - * - * Note that this is only sensible when the LOAD - * segments are contiguous (or overlapping). If - * used for LOADs that are far apart, this would - * cause the holes between LOADs to be mapped, - * running the risk of having the mapping fail, - * as it would be larger than the ELF file itself. - * - * As a result, only ET_DYN does this, since - * some ET_EXEC (e.g. ia64) may have large virtual - * memory holes between LOADs. - * - */ - total_size = total_mapping_size(elf_phdata, - elf_ex->e_phnum); - if (!total_size) { - retval = -EINVAL; - goto out_free_dentry; - } }
error = elf_load(bprm->file, load_bias + vaddr, elf_ppnt,
The p_align values in PT_LOAD were ignored for static PIE executables (i.e. ET_DYN without PT_INTERP). This is because there is no way to request a non-fixed mmap region with a specific alignment. ET_DYN with PT_INTERP uses a separate base address (ELF_ET_DYN_BASE) and binfmt_elf performs the ASLR itself, which means it can also apply alignment. For the mmap region, the address selection happens deep within the vm_mmap() implementation (when the requested address is 0).
The earlier attempt to implement this:
commit 9630f0d60fec ("fs/binfmt_elf: use PT_LOAD p_align values for static PIE") commit 925346c129da ("fs/binfmt_elf: fix PT_LOAD p_align values for loaders")
did not take into account the different base address origins, and were eventually reverted:
aeb7923733d1 ("revert "fs/binfmt_elf: use PT_LOAD p_align values for static PIE"")
In order to get the correct alignment from an mmap base, binfmt_elf must perform a 0-address load first, then tear down the mapping and perform alignment on the resulting address. Since this is slightly more overhead, only do this when it is needed (i.e. the alignment is not the default ELF alignment). This does, however, have the benefit of being able to use MAP_FIXED_NOREPLACE, to avoid potential collisions.
With this fixed, enable the static PIE self tests again.
Reported-by: H.J. Lu hjl.tools@gmail.com Closes: https://bugzilla.kernel.org/show_bug.cgi?id=215275 Signed-off-by: Kees Cook keescook@chromium.org --- Cc: H.J. Lu hjl.tools@gmail.com Cc: Mike Rapoport rppt@linux.ibm.com Cc: Rui Salvaterra rsalvaterra@gmail.com Cc: Victor Stinner vstinner@redhat.com Cc: Jan Palus jpalus@fastmail.com Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Christian Brauner brauner@kernel.org Cc: Jan Kara jack@suse.cz Cc: Eric Biederman ebiederm@xmission.com Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org --- fs/binfmt_elf.c | 42 +++++++++++++++++++++++---- tools/testing/selftests/exec/Makefile | 2 +- 2 files changed, 38 insertions(+), 6 deletions(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 56432e019d4e..cbb07a9c02d4 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -1088,10 +1088,13 @@ static int load_elf_binary(struct linux_binprm *bprm) goto out_free_dentry; }
+ /* Calculate any requested alignment. */ + alignment = maximum_alignment(elf_phdata, elf_ex->e_phnum); + /* * There are effectively two types of ET_DYN - * binaries: programs (i.e. PIE: ET_DYN with INTERP) - * and loaders (ET_DYN without INTERP, since they + * binaries: programs (i.e. PIE: ET_DYN with PT_INTERP) + * and loaders (ET_DYN without PT_INTERP, since they * _are_ the ELF interpreter). The loaders must * be loaded away from programs since the program * may otherwise collide with the loader (especially @@ -1111,15 +1114,44 @@ static int load_elf_binary(struct linux_binprm *bprm) * without MAP_FIXED nor MAP_FIXED_NOREPLACE). */ if (interpreter) { + /* On ET_DYN with PT_INTERP, we do the ASLR. */ load_bias = ELF_ET_DYN_BASE; if (current->flags & PF_RANDOMIZE) load_bias += arch_mmap_rnd(); - alignment = maximum_alignment(elf_phdata, elf_ex->e_phnum); + /* Adjust alignment as requested. */ if (alignment) load_bias &= ~(alignment - 1); elf_flags |= MAP_FIXED_NOREPLACE; - } else - load_bias = 0; + } else { + /* + * For ET_DYN without PT_INTERP, we rely on + * the architectures's (potentially ASLR) mmap + * base address (via a load_bias of 0). + * + * When a large alignment is requested, we + * must do the allocation at address "0" right + * now to discover where things will load so + * that we can adjust the resulting alignment. + * In this case (load_bias != 0), we can use + * MAP_FIXED_NOREPLACE to make sure the mapping + * doesn't collide with anything. + */ + if (alignment > ELF_MIN_ALIGN) { + load_bias = elf_load(bprm->file, 0, elf_ppnt, + elf_prot, elf_flags, total_size); + if (BAD_ADDR(load_bias)) { + retval = IS_ERR_VALUE(load_bias) ? + PTR_ERR((void*)load_bias) : -EINVAL; + goto out_free_dentry; + } + vm_munmap(load_bias, total_size); + /* Adjust alignment as requested. */ + if (alignment) + load_bias &= ~(alignment - 1); + elf_flags |= MAP_FIXED_NOREPLACE; + } else + load_bias = 0; + }
/* * Since load_bias is used for all subsequent loading diff --git a/tools/testing/selftests/exec/Makefile b/tools/testing/selftests/exec/Makefile index 619cff81d796..ab67d58cfab7 100644 --- a/tools/testing/selftests/exec/Makefile +++ b/tools/testing/selftests/exec/Makefile @@ -6,7 +6,7 @@ CFLAGS += -D_GNU_SOURCE ALIGNS := 0x1000 0x200000 0x1000000 ALIGN_PIES := $(patsubst %,load_address.%,$(ALIGNS)) ALIGN_STATIC_PIES := $(patsubst %,load_address.static.%,$(ALIGNS)) -ALIGNMENT_TESTS := $(ALIGN_PIES) +ALIGNMENT_TESTS := $(ALIGN_PIES) $(ALIGN_STATIC_PIES)
TEST_PROGS := binfmt_script.py TEST_GEN_PROGS := execveat non-regular $(ALIGNMENT_TESTS)
linux-kselftest-mirror@lists.linaro.org
-
John Hubbard -
Kees Cook