[PATCH v3 0/4] arm64: Enable BTI for the executable as well as the interpreter

[PATCH v3 0/4] arm64: Enable BTI for the executable as well as the interpreter

[Mark Brown]

Deployments of BTI on arm64 have run into issues interacting with
systemd's MemoryDenyWriteExecute feature.  Currently for dynamically
linked executables the kernel will only handle architecture specific
properties like BTI for the interpreter, the expectation is that the
interpreter will then handle any properties on the main executable.
For BTI this means remapping the executable segments PROT_EXEC |
PROT_BTI.

This interacts poorly with MemoryDenyWriteExecute since that is
implemented using a seccomp filter which prevents setting PROT_EXEC on
already mapped memory and lacks the context to be able to detect that
memory is already mapped with PROT_EXEC.  This series resolves this by
handling the BTI property for both the interpreter and the main
executable.

This does mean that we may get more code with BTI enabled if running on
a system without BTI support in the dynamic linker, this is expected to
be a safe configuration and testing seems to confirm that. It also
reduces the flexibility userspace has to disable BTI but it is expected
that for cases where there are problems which require BTI to be disabled
it is more likely that it will need to be disabled on a system level.

v3:
 - Fix passing of properties for parsing by the main executable.
 - Drop has_interp from arch_parse_elf_property().
 - Coding style tweaks.
v2:
 - Add a patch dropping has_interp from arch_adjust_elf_prot()
 - Fix bisection issue with static executables on arm64 in the first
   patch.

Mark Brown (4):
  elf: Allow architectures to parse properties on the main executable
  arm64: Enable BTI for main executable as well as the interpreter
  elf: Remove has_interp property from arch_adjust_elf_prot()
  elf: Remove has_interp property from arch_parse_elf_property()

 arch/arm64/include/asm/elf.h | 13 ++++++++++---
 arch/arm64/kernel/process.c  | 23 +++++++++++------------
 fs/binfmt_elf.c              | 33 ++++++++++++++++++++++++---------
 include/linux/elf.h          |  8 +++++---
 4 files changed, 50 insertions(+), 27 deletions(-)


base-commit: c4681547bcce777daf576925a966ffa824edd09d
-- 
2.20.1

[PATCH v3 0/4] arm64: Enable BTI for the executable as well as the interpreter

[Mark Brown]

Deployments of BTI on arm64 have run into issues interacting with
systemd's MemoryDenyWriteExecute feature.  Currently for dynamically
linked executables the kernel will only handle architecture specific
properties like BTI for the interpreter, the expectation is that the
interpreter will then handle any properties on the main executable.
For BTI this means remapping the executable segments PROT_EXEC |
PROT_BTI.

This interacts poorly with MemoryDenyWriteExecute since that is
implemented using a seccomp filter which prevents setting PROT_EXEC on
already mapped memory and lacks the context to be able to detect that
memory is already mapped with PROT_EXEC.  This series resolves this by
handling the BTI property for both the interpreter and the main
executable.

This does mean that we may get more code with BTI enabled if running on
a system without BTI support in the dynamic linker, this is expected to
be a safe configuration and testing seems to confirm that. It also
reduces the flexibility userspace has to disable BTI but it is expected
that for cases where there are problems which require BTI to be disabled
it is more likely that it will need to be disabled on a system level.

v3:
 - Fix passing of properties for parsing by the main executable.
 - Drop has_interp from arch_parse_elf_property().
 - Coding style tweaks.
v2:
 - Add a patch dropping has_interp from arch_adjust_elf_prot()
 - Fix bisection issue with static executables on arm64 in the first
   patch.

Mark Brown (4):
  elf: Allow architectures to parse properties on the main executable
  arm64: Enable BTI for main executable as well as the interpreter
  elf: Remove has_interp property from arch_adjust_elf_prot()
  elf: Remove has_interp property from arch_parse_elf_property()

 arch/arm64/include/asm/elf.h | 13 ++++++++++---
 arch/arm64/kernel/process.c  | 23 +++++++++++------------
 fs/binfmt_elf.c              | 33 ++++++++++++++++++++++++---------
 include/linux/elf.h          |  8 +++++---
 4 files changed, 50 insertions(+), 27 deletions(-)


base-commit: c4681547bcce777daf576925a966ffa824edd09d
-- 
2.20.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v3 1/4] elf: Allow architectures to parse properties on the main executable

[Mark Brown]

Currently the ELF code only attempts to parse properties on the image
that will start execution, either the interpreter or for statically linked
executables the main executable. The expectation is that any property
handling for the main executable will be done by the interpreter. This is
a bit inconsistent since we do map the executable and is causing problems
for the arm64 BTI support when used in conjunction with systemd's use of
seccomp to implement MemoryDenyWriteExecute which stops the dynamic linker
adjusting the permissions of executable segments.

Allow architectures to handle properties for both the dynamic linker and
main executable, adjusting arch_parse_elf_properties() to have an is_interp
flag as with arch_elf_adjust_prot() and calling it for both the main
executable and any intepreter.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/elf.h |  3 ++-
 fs/binfmt_elf.c              | 31 +++++++++++++++++++++++--------
 include/linux/elf.h          |  4 +++-
 3 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 8d1c8dcb87fd..a488a1329b16 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -261,6 +261,7 @@ struct arch_elf_state {
 
 static inline int arch_parse_elf_property(u32 type, const void *data,
 					  size_t datasz, bool compat,
+					  bool has_interp, bool is_interp,
 					  struct arch_elf_state *arch)
 {
 	/* No known properties for AArch32 yet */
@@ -273,7 +274,7 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
 		if (datasz != sizeof(*p))
 			return -ENOEXEC;
 
-		if (system_supports_bti() &&
+		if (system_supports_bti() && has_interp == is_interp &&
 		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
 			arch->flags |= ARM64_ELF_BTI;
 	}
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 187b3f2b9202..c0d4f35c80f6 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -716,8 +716,9 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
  */
 
 static int parse_elf_property(const char *data, size_t *off, size_t datasz,
-			      struct arch_elf_state *arch,
-			      bool have_prev_type, u32 *prev_type)
+			      struct arch_elf_state *arch, bool has_interp,
+			      bool is_interp, bool have_prev_type,
+			      u32 *prev_type)
 {
 	size_t o, step;
 	const struct gnu_property *pr;
@@ -751,7 +752,8 @@ static int parse_elf_property(const char *data, size_t *off, size_t datasz,
 	*prev_type = pr->pr_type;
 
 	ret = arch_parse_elf_property(pr->pr_type, data + o,
-				      pr->pr_datasz, ELF_COMPAT, arch);
+				      pr->pr_datasz, ELF_COMPAT,
+				      has_interp, is_interp, arch);
 	if (ret)
 		return ret;
 
@@ -764,6 +766,7 @@ static int parse_elf_property(const char *data, size_t *off, size_t datasz,
 #define NOTE_NAME_SZ (sizeof(GNU_PROPERTY_TYPE_0_NAME))
 
 static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
+				bool has_interp, bool is_interp,
 				struct arch_elf_state *arch)
 {
 	union {
@@ -813,7 +816,8 @@ static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
 	have_prev_type = false;
 	do {
 		ret = parse_elf_property(note.data, &off, datasz, arch,
-					 have_prev_type, &prev_type);
+					 has_interp, is_interp, have_prev_type,
+					 &prev_type);
 		have_prev_type = true;
 	} while (!ret);
 
@@ -828,6 +832,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	unsigned long error;
 	struct elf_phdr *elf_ppnt, *elf_phdata, *interp_elf_phdata = NULL;
 	struct elf_phdr *elf_property_phdata = NULL;
+	struct elf_phdr *interp_elf_property_phdata = NULL;
 	unsigned long elf_bss, elf_brk;
 	int bss_prot = 0;
 	int retval, i;
@@ -936,6 +941,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
 				executable_stack = EXSTACK_DISABLE_X;
 			break;
 
+		case PT_GNU_PROPERTY:
+			elf_property_phdata = elf_ppnt;
+			break;
+
 		case PT_LOPROC ... PT_HIPROC:
 			retval = arch_elf_pt_proc(elf_ex, elf_ppnt,
 						  bprm->file, false,
@@ -963,12 +972,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
 			goto out_free_dentry;
 
 		/* Pass PT_LOPROC..PT_HIPROC headers to arch code */
-		elf_property_phdata = NULL;
 		elf_ppnt = interp_elf_phdata;
 		for (i = 0; i < interp_elf_ex->e_phnum; i++, elf_ppnt++)
 			switch (elf_ppnt->p_type) {
 			case PT_GNU_PROPERTY:
-				elf_property_phdata = elf_ppnt;
+				interp_elf_property_phdata = elf_ppnt;
 				break;
 
 			case PT_LOPROC ... PT_HIPROC:
@@ -979,10 +987,17 @@ static int load_elf_binary(struct linux_binprm *bprm)
 					goto out_free_dentry;
 				break;
 			}
+
+		retval = parse_elf_properties(interpreter,
+					      interp_elf_property_phdata,
+					      true, true, &arch_state);
+		if (retval)
+			goto out_free_dentry;
+
 	}
 
-	retval = parse_elf_properties(interpreter ?: bprm->file,
-				      elf_property_phdata, &arch_state);
+	retval = parse_elf_properties(bprm->file, elf_property_phdata,
+				      interpreter != NULL, false, &arch_state);
 	if (retval)
 		goto out_free_dentry;
 
diff --git a/include/linux/elf.h b/include/linux/elf.h
index c9a46c4e183b..1c45ecf29147 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -88,13 +88,15 @@ struct arch_elf_state;
 #ifndef CONFIG_ARCH_USE_GNU_PROPERTY
 static inline int arch_parse_elf_property(u32 type, const void *data,
 					  size_t datasz, bool compat,
+					  bool has_interp, bool is_interp,
 					  struct arch_elf_state *arch)
 {
 	return 0;
 }
 #else
 extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
-				   bool compat, struct arch_elf_state *arch);
+				   bool compat, bool has_interp, bool is_interp,
+				   struct arch_elf_state *arch);
 #endif
 
 #ifdef CONFIG_ARCH_HAVE_ELF_PROT
-- 
2.20.1

[PATCH v3 1/4] elf: Allow architectures to parse properties on the main executable

[Mark Brown]

Currently the ELF code only attempts to parse properties on the image
that will start execution, either the interpreter or for statically linked
executables the main executable. The expectation is that any property
handling for the main executable will be done by the interpreter. This is
a bit inconsistent since we do map the executable and is causing problems
for the arm64 BTI support when used in conjunction with systemd's use of
seccomp to implement MemoryDenyWriteExecute which stops the dynamic linker
adjusting the permissions of executable segments.

Allow architectures to handle properties for both the dynamic linker and
main executable, adjusting arch_parse_elf_properties() to have an is_interp
flag as with arch_elf_adjust_prot() and calling it for both the main
executable and any intepreter.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/elf.h |  3 ++-
 fs/binfmt_elf.c              | 31 +++++++++++++++++++++++--------
 include/linux/elf.h          |  4 +++-
 3 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 8d1c8dcb87fd..a488a1329b16 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -261,6 +261,7 @@ struct arch_elf_state {
 
 static inline int arch_parse_elf_property(u32 type, const void *data,
 					  size_t datasz, bool compat,
+					  bool has_interp, bool is_interp,
 					  struct arch_elf_state *arch)
 {
 	/* No known properties for AArch32 yet */
@@ -273,7 +274,7 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
 		if (datasz != sizeof(*p))
 			return -ENOEXEC;
 
-		if (system_supports_bti() &&
+		if (system_supports_bti() && has_interp == is_interp &&
 		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
 			arch->flags |= ARM64_ELF_BTI;
 	}
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 187b3f2b9202..c0d4f35c80f6 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -716,8 +716,9 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
  */
 
 static int parse_elf_property(const char *data, size_t *off, size_t datasz,
-			      struct arch_elf_state *arch,
-			      bool have_prev_type, u32 *prev_type)
+			      struct arch_elf_state *arch, bool has_interp,
+			      bool is_interp, bool have_prev_type,
+			      u32 *prev_type)
 {
 	size_t o, step;
 	const struct gnu_property *pr;
@@ -751,7 +752,8 @@ static int parse_elf_property(const char *data, size_t *off, size_t datasz,
 	*prev_type = pr->pr_type;
 
 	ret = arch_parse_elf_property(pr->pr_type, data + o,
-				      pr->pr_datasz, ELF_COMPAT, arch);
+				      pr->pr_datasz, ELF_COMPAT,
+				      has_interp, is_interp, arch);
 	if (ret)
 		return ret;
 
@@ -764,6 +766,7 @@ static int parse_elf_property(const char *data, size_t *off, size_t datasz,
 #define NOTE_NAME_SZ (sizeof(GNU_PROPERTY_TYPE_0_NAME))
 
 static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
+				bool has_interp, bool is_interp,
 				struct arch_elf_state *arch)
 {
 	union {
@@ -813,7 +816,8 @@ static int parse_elf_properties(struct file *f, const struct elf_phdr *phdr,
 	have_prev_type = false;
 	do {
 		ret = parse_elf_property(note.data, &off, datasz, arch,
-					 have_prev_type, &prev_type);
+					 has_interp, is_interp, have_prev_type,
+					 &prev_type);
 		have_prev_type = true;
 	} while (!ret);
 
@@ -828,6 +832,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	unsigned long error;
 	struct elf_phdr *elf_ppnt, *elf_phdata, *interp_elf_phdata = NULL;
 	struct elf_phdr *elf_property_phdata = NULL;
+	struct elf_phdr *interp_elf_property_phdata = NULL;
 	unsigned long elf_bss, elf_brk;
 	int bss_prot = 0;
 	int retval, i;
@@ -936,6 +941,10 @@ static int load_elf_binary(struct linux_binprm *bprm)
 				executable_stack = EXSTACK_DISABLE_X;
 			break;
 
+		case PT_GNU_PROPERTY:
+			elf_property_phdata = elf_ppnt;
+			break;
+
 		case PT_LOPROC ... PT_HIPROC:
 			retval = arch_elf_pt_proc(elf_ex, elf_ppnt,
 						  bprm->file, false,
@@ -963,12 +972,11 @@ static int load_elf_binary(struct linux_binprm *bprm)
 			goto out_free_dentry;
 
 		/* Pass PT_LOPROC..PT_HIPROC headers to arch code */
-		elf_property_phdata = NULL;
 		elf_ppnt = interp_elf_phdata;
 		for (i = 0; i < interp_elf_ex->e_phnum; i++, elf_ppnt++)
 			switch (elf_ppnt->p_type) {
 			case PT_GNU_PROPERTY:
-				elf_property_phdata = elf_ppnt;
+				interp_elf_property_phdata = elf_ppnt;
 				break;
 
 			case PT_LOPROC ... PT_HIPROC:
@@ -979,10 +987,17 @@ static int load_elf_binary(struct linux_binprm *bprm)
 					goto out_free_dentry;
 				break;
 			}
+
+		retval = parse_elf_properties(interpreter,
+					      interp_elf_property_phdata,
+					      true, true, &arch_state);
+		if (retval)
+			goto out_free_dentry;
+
 	}
 
-	retval = parse_elf_properties(interpreter ?: bprm->file,
-				      elf_property_phdata, &arch_state);
+	retval = parse_elf_properties(bprm->file, elf_property_phdata,
+				      interpreter != NULL, false, &arch_state);
 	if (retval)
 		goto out_free_dentry;
 
diff --git a/include/linux/elf.h b/include/linux/elf.h
index c9a46c4e183b..1c45ecf29147 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -88,13 +88,15 @@ struct arch_elf_state;
 #ifndef CONFIG_ARCH_USE_GNU_PROPERTY
 static inline int arch_parse_elf_property(u32 type, const void *data,
 					  size_t datasz, bool compat,
+					  bool has_interp, bool is_interp,
 					  struct arch_elf_state *arch)
 {
 	return 0;
 }
 #else
 extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
-				   bool compat, struct arch_elf_state *arch);
+				   bool compat, bool has_interp, bool is_interp,
+				   struct arch_elf_state *arch);
 #endif
 
 #ifdef CONFIG_ARCH_HAVE_ELF_PROT
-- 
2.20.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

[PATCH v3 2/4] arm64: Enable BTI for main executable as well as the interpreter

[Mark Brown]

Currently for dynamically linked ELF executables we only enable BTI for
the interpreter, expecting the interpreter to do this for the main
executable. This is a bit inconsistent since we do map main executable and
is causing issues with systemd's MemoryDenyWriteExecute feature which is
implemented using a seccomp filter which prevents setting PROT_EXEC on
already mapped memory and lacks the context to be able to detect that
memory is already mapped with PROT_EXEC.

Resolve this by checking the BTI property for the main executable and
enabling BTI if it is present when doing the initial mapping. This does
mean that we may get more code with BTI enabled if running on a system
without BTI support in the dynamic linker, this is expected to be a safe
configuration and testing seems to confirm that. It also reduces the
flexibility userspace has to disable BTI but it is expected that for cases
where there are problems which require BTI to be disabled it is more likely
that it will need to be disabled on a system level.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
---
 arch/arm64/include/asm/elf.h | 14 ++++++++++----
 arch/arm64/kernel/process.c  | 23 +++++++++++------------
 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index a488a1329b16..9f86dbce2680 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -253,7 +253,8 @@ struct arch_elf_state {
 	int flags;
 };
 
-#define ARM64_ELF_BTI		(1 << 0)
+#define ARM64_ELF_INTERP_BTI		(1 << 0)
+#define ARM64_ELF_EXEC_BTI		(1 << 1)
 
 #define INIT_ARCH_ELF_STATE {			\
 	.flags = 0,				\
@@ -274,9 +275,14 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
 		if (datasz != sizeof(*p))
 			return -ENOEXEC;
 
-		if (system_supports_bti() && has_interp == is_interp &&
-		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
-			arch->flags |= ARM64_ELF_BTI;
+		if (system_supports_bti() &&
+		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
+			if (is_interp) {
+				arch->flags |= ARM64_ELF_INTERP_BTI;
+			} else {
+				arch->flags |= ARM64_ELF_EXEC_BTI;
+			}
+		}
 	}
 
 	return 0;
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index b4bb67f17a2c..21f1f0997c43 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -741,21 +741,20 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void)
 }
 
 #ifdef CONFIG_BINFMT_ELF
-int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
-			 bool has_interp, bool is_interp)
+static inline int arm64_elf_bti_flag(bool is_interp)
 {
-	/*
-	 * For dynamically linked executables the interpreter is
-	 * responsible for setting PROT_BTI on everything except
-	 * itself.
-	 */
-	if (is_interp != has_interp)
-		return prot;
+	if (is_interp)
+		return ARM64_ELF_INTERP_BTI;
+	else
+		return ARM64_ELF_EXEC_BTI;
+}
 
-	if (!(state->flags & ARM64_ELF_BTI))
-		return prot;
 
-	if (prot & PROT_EXEC)
+int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
+			 bool has_interp, bool is_interp)
+{
+	if ((prot & PROT_EXEC) &&
+	    (state->flags & arm64_elf_bti_flag(is_interp)))
 		prot |= PROT_BTI;
 
 	return prot;
-- 
2.20.1

[PATCH v3 2/4] arm64: Enable BTI for main executable as well as the interpreter

[Mark Brown]

Currently for dynamically linked ELF executables we only enable BTI for
the interpreter, expecting the interpreter to do this for the main
executable. This is a bit inconsistent since we do map main executable and
is causing issues with systemd's MemoryDenyWriteExecute feature which is
implemented using a seccomp filter which prevents setting PROT_EXEC on
already mapped memory and lacks the context to be able to detect that
memory is already mapped with PROT_EXEC.

Resolve this by checking the BTI property for the main executable and
enabling BTI if it is present when doing the initial mapping. This does
mean that we may get more code with BTI enabled if running on a system
without BTI support in the dynamic linker, this is expected to be a safe
configuration and testing seems to confirm that. It also reduces the
flexibility userspace has to disable BTI but it is expected that for cases
where there are problems which require BTI to be disabled it is more likely
that it will need to be disabled on a system level.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
---
 arch/arm64/include/asm/elf.h | 14 ++++++++++----
 arch/arm64/kernel/process.c  | 23 +++++++++++------------
 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index a488a1329b16..9f86dbce2680 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -253,7 +253,8 @@ struct arch_elf_state {
 	int flags;
 };
 
-#define ARM64_ELF_BTI		(1 << 0)
+#define ARM64_ELF_INTERP_BTI		(1 << 0)
+#define ARM64_ELF_EXEC_BTI		(1 << 1)
 
 #define INIT_ARCH_ELF_STATE {			\
 	.flags = 0,				\
@@ -274,9 +275,14 @@ static inline int arch_parse_elf_property(u32 type, const void *data,
 		if (datasz != sizeof(*p))
 			return -ENOEXEC;
 
-		if (system_supports_bti() && has_interp == is_interp &&
-		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI))
-			arch->flags |= ARM64_ELF_BTI;
+		if (system_supports_bti() &&
+		    (*p & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
+			if (is_interp) {
+				arch->flags |= ARM64_ELF_INTERP_BTI;
+			} else {
+				arch->flags |= ARM64_ELF_EXEC_BTI;
+			}
+		}
 	}
 
 	return 0;
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index b4bb67f17a2c..21f1f0997c43 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -741,21 +741,20 @@ asmlinkage void __sched arm64_preempt_schedule_irq(void)
 }
 
 #ifdef CONFIG_BINFMT_ELF
-int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
-			 bool has_interp, bool is_interp)
+static inline int arm64_elf_bti_flag(bool is_interp)
 {
-	/*
-	 * For dynamically linked executables the interpreter is
-	 * responsible for setting PROT_BTI on everything except
-	 * itself.
-	 */
-	if (is_interp != has_interp)
-		return prot;
+	if (is_interp)
+		return ARM64_ELF_INTERP_BTI;
+	else
+		return ARM64_ELF_EXEC_BTI;
+}
 
-	if (!(state->flags & ARM64_ELF_BTI))
-		return prot;
 
-	if (prot & PROT_EXEC)
+int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
+			 bool has_interp, bool is_interp)
+{
+	if ((prot & PROT_EXEC) &&
+	    (state->flags & arm64_elf_bti_flag(is_interp)))
 		prot |= PROT_BTI;
 
 	return prot;
-- 
2.20.1


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[PATCH v3 3/4] elf: Remove has_interp property from arch_adjust_elf_prot()

[Mark Brown]

Since we have added an is_interp flag to arch_parse_elf_property() we can
drop the has_interp flag from arch_elf_adjust_prot(), the only user was
the arm64 code which no longer needs it and any future users will be able
to use arch_parse_elf_properties() to determine if an interpreter is in
use.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/kernel/process.c | 2 +-
 fs/binfmt_elf.c             | 2 +-
 include/linux/elf.h         | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 21f1f0997c43..2b952593534a 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -751,7 +751,7 @@ static inline int arm64_elf_bti_flag(bool is_interp)
 
 
 int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
-			 bool has_interp, bool is_interp)
+			 bool is_interp)
 {
 	if ((prot & PROT_EXEC) &&
 	    (state->flags & arm64_elf_bti_flag(is_interp)))
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index c0d4f35c80f6..ffe38d54308b 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -580,7 +580,7 @@ static inline int make_prot(u32 p_flags, struct arch_elf_state *arch_state,
 	if (p_flags & PF_X)
 		prot |= PROT_EXEC;
 
-	return arch_elf_adjust_prot(prot, arch_state, has_interp, is_interp);
+	return arch_elf_adjust_prot(prot, arch_state, is_interp);
 }
 
 /* This is much more generalized than the library routine read function,
diff --git a/include/linux/elf.h b/include/linux/elf.h
index 1c45ecf29147..d8392531899d 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -101,11 +101,11 @@ extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
 
 #ifdef CONFIG_ARCH_HAVE_ELF_PROT
 int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
-			 bool has_interp, bool is_interp);
+			 bool is_interp);
 #else
 static inline int arch_elf_adjust_prot(int prot,
 				       const struct arch_elf_state *state,
-				       bool has_interp, bool is_interp)
+				       bool is_interp)
 {
 	return prot;
 }
-- 
2.20.1

[PATCH v3 3/4] elf: Remove has_interp property from arch_adjust_elf_prot()

[Mark Brown]

Since we have added an is_interp flag to arch_parse_elf_property() we can
drop the has_interp flag from arch_elf_adjust_prot(), the only user was
the arm64 code which no longer needs it and any future users will be able
to use arch_parse_elf_properties() to determine if an interpreter is in
use.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/kernel/process.c | 2 +-
 fs/binfmt_elf.c             | 2 +-
 include/linux/elf.h         | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 21f1f0997c43..2b952593534a 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -751,7 +751,7 @@ static inline int arm64_elf_bti_flag(bool is_interp)
 
 
 int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
-			 bool has_interp, bool is_interp)
+			 bool is_interp)
 {
 	if ((prot & PROT_EXEC) &&
 	    (state->flags & arm64_elf_bti_flag(is_interp)))
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index c0d4f35c80f6..ffe38d54308b 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -580,7 +580,7 @@ static inline int make_prot(u32 p_flags, struct arch_elf_state *arch_state,
 	if (p_flags & PF_X)
 		prot |= PROT_EXEC;
 
-	return arch_elf_adjust_prot(prot, arch_state, has_interp, is_interp);
+	return arch_elf_adjust_prot(prot, arch_state, is_interp);
 }
 
 /* This is much more generalized than the library routine read function,
diff --git a/include/linux/elf.h b/include/linux/elf.h
index 1c45ecf29147..d8392531899d 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -101,11 +101,11 @@ extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
 
 #ifdef CONFIG_ARCH_HAVE_ELF_PROT
 int arch_elf_adjust_prot(int prot, const struct arch_elf_state *state,
-			 bool has_interp, bool is_interp);
+			 bool is_interp);
 #else
 static inline int arch_elf_adjust_prot(int prot,
 				       const struct arch_elf_state *state,
-				       bool has_interp, bool is_interp)
+				       bool is_interp)
 {
 	return prot;
 }
-- 
2.20.1


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[PATCH v3 4/4] elf: Remove has_interp property from arch_parse_elf_property()

[Mark Brown]

Since all current users of arch_parse_elf_property() are able to treat the
interpreter and main executable orthogonaly the has_interp argument is now
redundant so remove it.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/elf.h | 2 +-
 fs/binfmt_elf.c              | 2 +-
 include/linux/elf.h          | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 9f86dbce2680..a6e9032b951a 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -262,7 +262,7 @@ struct arch_elf_state {
 
 static inline int arch_parse_elf_property(u32 type, const void *data,
 					  size_t datasz, bool compat,
-					  bool has_interp, bool is_interp,
+					  bool is_interp,
 					  struct arch_elf_state *arch)
 {
 	/* No known properties for AArch32 yet */
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index ffe38d54308b..5509ae63c2e1 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -753,7 +753,7 @@ static int parse_elf_property(const char *data, size_t *off, size_t datasz,
 
 	ret = arch_parse_elf_property(pr->pr_type, data + o,
 				      pr->pr_datasz, ELF_COMPAT,
-				      has_interp, is_interp, arch);
+				      is_interp, arch);
 	if (ret)
 		return ret;
 
diff --git a/include/linux/elf.h b/include/linux/elf.h
index d8392531899d..cdb080d4b34a 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -88,14 +88,14 @@ struct arch_elf_state;
 #ifndef CONFIG_ARCH_USE_GNU_PROPERTY
 static inline int arch_parse_elf_property(u32 type, const void *data,
 					  size_t datasz, bool compat,
-					  bool has_interp, bool is_interp,
+					  bool is_interp,
 					  struct arch_elf_state *arch)
 {
 	return 0;
 }
 #else
 extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
-				   bool compat, bool has_interp, bool is_interp,
+				   bool compat, bool is_interp,
 				   struct arch_elf_state *arch);
 #endif
 
-- 
2.20.1

[PATCH v3 4/4] elf: Remove has_interp property from arch_parse_elf_property()

[Mark Brown]

Since all current users of arch_parse_elf_property() are able to treat the
interpreter and main executable orthogonaly the has_interp argument is now
redundant so remove it.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 arch/arm64/include/asm/elf.h | 2 +-
 fs/binfmt_elf.c              | 2 +-
 include/linux/elf.h          | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 9f86dbce2680..a6e9032b951a 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -262,7 +262,7 @@ struct arch_elf_state {
 
 static inline int arch_parse_elf_property(u32 type, const void *data,
 					  size_t datasz, bool compat,
-					  bool has_interp, bool is_interp,
+					  bool is_interp,
 					  struct arch_elf_state *arch)
 {
 	/* No known properties for AArch32 yet */
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index ffe38d54308b..5509ae63c2e1 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -753,7 +753,7 @@ static int parse_elf_property(const char *data, size_t *off, size_t datasz,
 
 	ret = arch_parse_elf_property(pr->pr_type, data + o,
 				      pr->pr_datasz, ELF_COMPAT,
-				      has_interp, is_interp, arch);
+				      is_interp, arch);
 	if (ret)
 		return ret;
 
diff --git a/include/linux/elf.h b/include/linux/elf.h
index d8392531899d..cdb080d4b34a 100644
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -88,14 +88,14 @@ struct arch_elf_state;
 #ifndef CONFIG_ARCH_USE_GNU_PROPERTY
 static inline int arch_parse_elf_property(u32 type, const void *data,
 					  size_t datasz, bool compat,
-					  bool has_interp, bool is_interp,
+					  bool is_interp,
 					  struct arch_elf_state *arch)
 {
 	return 0;
 }
 #else
 extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
-				   bool compat, bool has_interp, bool is_interp,
+				   bool compat, bool is_interp,
 				   struct arch_elf_state *arch);
 #endif
 
-- 
2.20.1


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Re: [PATCH v3 0/4] arm64: Enable BTI for the executable as well as the interpreter

[Jeremy Linton]

Hi,

On 6/14/21 5:32 PM, Mark Brown wrote:
> Deployments of BTI on arm64 have run into issues interacting with
> systemd's MemoryDenyWriteExecute feature.  Currently for dynamically
> linked executables the kernel will only handle architecture specific
> properties like BTI for the interpreter, the expectation is that the
> interpreter will then handle any properties on the main executable.
> For BTI this means remapping the executable segments PROT_EXEC |
> PROT_BTI.
> 
> This interacts poorly with MemoryDenyWriteExecute since that is
> implemented using a seccomp filter which prevents setting PROT_EXEC on
> already mapped memory and lacks the context to be able to detect that
> memory is already mapped with PROT_EXEC.  This series resolves this by
> handling the BTI property for both the interpreter and the main
> executable.
> 
> This does mean that we may get more code with BTI enabled if running on
> a system without BTI support in the dynamic linker, this is expected to
> be a safe configuration and testing seems to confirm that. It also
> reduces the flexibility userspace has to disable BTI but it is expected
> that for cases where there are problems which require BTI to be disabled
> it is more likely that it will need to be disabled on a system level.

It looks like its working as expected now (the previously detailed test 
is now failing) in a MDWE enviroment, and the smaps/etc looks as 
expected too.

Thanks for fixing this!

tested-by: Jeremy Linton <jeremy.linton@arm.com>


> 
> v3:
>   - Fix passing of properties for parsing by the main executable.
>   - Drop has_interp from arch_parse_elf_property().
>   - Coding style tweaks.
> v2:
>   - Add a patch dropping has_interp from arch_adjust_elf_prot()
>   - Fix bisection issue with static executables on arm64 in the first
>     patch.
> 
> Mark Brown (4):
>    elf: Allow architectures to parse properties on the main executable
>    arm64: Enable BTI for main executable as well as the interpreter
>    elf: Remove has_interp property from arch_adjust_elf_prot()
>    elf: Remove has_interp property from arch_parse_elf_property()
> 
>   arch/arm64/include/asm/elf.h | 13 ++++++++++---
>   arch/arm64/kernel/process.c  | 23 +++++++++++------------
>   fs/binfmt_elf.c              | 33 ++++++++++++++++++++++++---------
>   include/linux/elf.h          |  8 +++++---
>   4 files changed, 50 insertions(+), 27 deletions(-)
> 
> 
> base-commit: c4681547bcce777daf576925a966ffa824edd09d
> 

Re: [PATCH v3 0/4] arm64: Enable BTI for the executable as well as the interpreter

[Jeremy Linton]

Hi,

On 6/14/21 5:32 PM, Mark Brown wrote:
> Deployments of BTI on arm64 have run into issues interacting with
> systemd's MemoryDenyWriteExecute feature.  Currently for dynamically
> linked executables the kernel will only handle architecture specific
> properties like BTI for the interpreter, the expectation is that the
> interpreter will then handle any properties on the main executable.
> For BTI this means remapping the executable segments PROT_EXEC |
> PROT_BTI.
> 
> This interacts poorly with MemoryDenyWriteExecute since that is
> implemented using a seccomp filter which prevents setting PROT_EXEC on
> already mapped memory and lacks the context to be able to detect that
> memory is already mapped with PROT_EXEC.  This series resolves this by
> handling the BTI property for both the interpreter and the main
> executable.
> 
> This does mean that we may get more code with BTI enabled if running on
> a system without BTI support in the dynamic linker, this is expected to
> be a safe configuration and testing seems to confirm that. It also
> reduces the flexibility userspace has to disable BTI but it is expected
> that for cases where there are problems which require BTI to be disabled
> it is more likely that it will need to be disabled on a system level.

It looks like its working as expected now (the previously detailed test 
is now failing) in a MDWE enviroment, and the smaps/etc looks as 
expected too.

Thanks for fixing this!

tested-by: Jeremy Linton <jeremy.linton@arm.com>


> 
> v3:
>   - Fix passing of properties for parsing by the main executable.
>   - Drop has_interp from arch_parse_elf_property().
>   - Coding style tweaks.
> v2:
>   - Add a patch dropping has_interp from arch_adjust_elf_prot()
>   - Fix bisection issue with static executables on arm64 in the first
>     patch.
> 
> Mark Brown (4):
>    elf: Allow architectures to parse properties on the main executable
>    arm64: Enable BTI for main executable as well as the interpreter
>    elf: Remove has_interp property from arch_adjust_elf_prot()
>    elf: Remove has_interp property from arch_parse_elf_property()
> 
>   arch/arm64/include/asm/elf.h | 13 ++++++++++---
>   arch/arm64/kernel/process.c  | 23 +++++++++++------------
>   fs/binfmt_elf.c              | 33 ++++++++++++++++++++++++---------
>   include/linux/elf.h          |  8 +++++---
>   4 files changed, 50 insertions(+), 27 deletions(-)
> 
> 
> base-commit: c4681547bcce777daf576925a966ffa824edd09d
> 


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