elf: Allow arch to tweak initial mmap prot flags

An arch may want to tweak the mmap prot flags for an
ELFexecutable's initial mappings.  For example, arm64 is going to
need to add PROT_BTI for executable pages in an ELF process whose
executable is marked as using Branch Target Identification (an
ARMv8.5-A control flow integrity feature).

So that this can be done in a generic way, add a hook
arch_elf_adjust_prot() to modify the prot flags as desired: arches
can select CONFIG_HAVE_ELF_PROT and implement their own backend
where necessary.

By default, leave the prot flags unchanged.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
index d2cfe0729a73fe77eb6870a764d7cacf16e10f8c..2358368319b8a0e10e805b6b80e94fc311e3df36 100644 (file)
--- a/fs/Kconfig.binfmt
+++ b/fs/Kconfig.binfmt
@@ -36,6 +36,9 @@ config COMPAT_BINFMT_ELF
 config ARCH_BINFMT_ELF_STATE
        bool
 
+config ARCH_HAVE_ELF_PROT
+       bool
+
 config ARCH_USE_GNU_PROPERTY
        bool
 

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 1fb67e506b68b90ec80d53c69af8381aed933689..cceb29d6ef1d9ff14c0f4eab0b811fee1c0db786 100644 (file)
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -544,7 +544,8 @@ static inline int arch_check_elf(struct elfhdr *ehdr, bool has_interp,
 
 #endif /* !CONFIG_ARCH_BINFMT_ELF_STATE */
 
-static inline int make_prot(u32 p_flags)
+static inline int make_prot(u32 p_flags, struct arch_elf_state *arch_state,
+                           bool has_interp, bool is_interp)
 {
        int prot = 0;
 
@@ -554,7 +555,8 @@ static inline int make_prot(u32 p_flags)
                prot |= PROT_WRITE;
        if (p_flags & PF_X)
                prot |= PROT_EXEC;
-       return prot;
+
+       return arch_elf_adjust_prot(prot, arch_state, has_interp, is_interp);
 }
 
 /* This is much more generalized than the library routine read function,
@@ -564,7 +566,8 @@ static inline int make_prot(u32 p_flags)
 
 static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
                struct file *interpreter,
-               unsigned long no_base, struct elf_phdr *interp_elf_phdata)
+               unsigned long no_base, struct elf_phdr *interp_elf_phdata,
+               struct arch_elf_state *arch_state)
 {
        struct elf_phdr *eppnt;
        unsigned long load_addr = 0;
@@ -596,7 +599,8 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
        for (i = 0; i < interp_elf_ex->e_phnum; i++, eppnt++) {
                if (eppnt->p_type == PT_LOAD) {
                        int elf_type = MAP_PRIVATE | MAP_DENYWRITE;
-                       int elf_prot = make_prot(eppnt->p_flags);
+                       int elf_prot = make_prot(eppnt->p_flags, arch_state,
+                                                true, true);
                        unsigned long vaddr = 0;
                        unsigned long k, map_addr;
 
@@ -1041,7 +1045,8 @@ out_free_interp:
                        }
                }
 
-               elf_prot = make_prot(elf_ppnt->p_flags);
+               elf_prot = make_prot(elf_ppnt->p_flags, &arch_state,
+                                    !!interpreter, false);
 
                elf_flags = MAP_PRIVATE | MAP_DENYWRITE | MAP_EXECUTABLE;
 
@@ -1184,7 +1189,8 @@ out_free_interp:
        if (interpreter) {
                elf_entry = load_elf_interp(&loc->interp_elf_ex,
                                            interpreter,
-                                           load_bias, interp_elf_phdata);
+                                           load_bias, interp_elf_phdata,
+                                           &arch_state);
                if (!IS_ERR((void *)elf_entry)) {
                        /*
                         * load_elf_interp() returns relocation

diff --git a/include/linux/elf.h b/include/linux/elf.h
index db5113479f5e9398bce2f1b135d765509c17fc20..5d5b0321da0bd81db3afa2bbe802252ca7e58a94 100644 (file)
--- a/include/linux/elf.h
+++ b/include/linux/elf.h
@@ -87,4 +87,16 @@ extern int arch_parse_elf_property(u32 type, const void *data, size_t datasz,
                                   bool compat, struct arch_elf_state *arch);
 #endif
 
+#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);
+#else
+static inline int arch_elf_adjust_prot(int prot,
+                                      const struct arch_elf_state *state,
+                                      bool has_interp, bool is_interp)
+{
+       return prot;
+}
+#endif
+
 #endif /* _LINUX_ELF_H */