linux-kernel - [PATCH -mm] elf: extract PROT

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Date:   Thu, 18 Apr 2019 00:34:13 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH -mm] elf: extract PROT_* calculations

There are 2 places where mapping protections are calculated: one for
executable, another one for interpreter -- take them out.

ELF read and execute permissions are interchanged with Linux PROT_READ
and PROT_EXEC, microoptimizations are welcome!

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 fs/binfmt_elf.c |   30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -524,6 +524,19 @@ 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)
+{
+	int prot = 0;
+
+	if (p_flags & PF_R)
+		prot |= PROT_READ;
+	if (p_flags & PF_W)
+		prot |= PROT_WRITE;
+	if (p_flags & PF_X)
+		prot |= PROT_EXEC;
+	return prot;
+}
+
 /* This is much more generalized than the library routine read function,
    so we keep this separate.  Technically the library read function
    is only provided so that we can read a.out libraries that have
@@ -563,16 +576,10 @@ 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 = 0;
+			int elf_prot = make_prot(eppnt->p_flags);
 			unsigned long vaddr = 0;
 			unsigned long k, map_addr;
 
-			if (eppnt->p_flags & PF_R)
-		    		elf_prot = PROT_READ;
-			if (eppnt->p_flags & PF_W)
-				elf_prot |= PROT_WRITE;
-			if (eppnt->p_flags & PF_X)
-				elf_prot |= PROT_EXEC;
 			vaddr = eppnt->p_vaddr;
 			if (interp_elf_ex->e_type == ET_EXEC || load_addr_set)
 				elf_type |= MAP_FIXED_NOREPLACE;
@@ -891,7 +898,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 	   the correct location in memory. */
 	for(i = 0, elf_ppnt = elf_phdata;
 	    i < loc->elf_ex.e_phnum; i++, elf_ppnt++) {
-		int elf_prot = 0, elf_flags, elf_fixed = MAP_FIXED_NOREPLACE;
+		int elf_prot, elf_flags, elf_fixed = MAP_FIXED_NOREPLACE;
 		unsigned long k, vaddr;
 		unsigned long total_size = 0;
 
@@ -932,12 +939,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 			elf_fixed = MAP_FIXED;
 		}
 
-		if (elf_ppnt->p_flags & PF_R)
-			elf_prot |= PROT_READ;
-		if (elf_ppnt->p_flags & PF_W)
-			elf_prot |= PROT_WRITE;
-		if (elf_ppnt->p_flags & PF_X)
-			elf_prot |= PROT_EXEC;
+		elf_prot = make_prot(elf_ppnt->p_flags);
 
 		elf_flags = MAP_PRIVATE | MAP_DENYWRITE | MAP_EXECUTABLE;