[PATCH v3 1/2] aarch64: align address for BTI protection [BZ #26988]

From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: libc-alpha@sourceware.org
Cc: Mark Rutland <mark.rutland@arm.com>,
	kernel-hardening@lists.openwall.com,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org,
	Jeremy Linton <jeremy.linton@arm.com>,
	Mark Brown <broonie@kernel.org>,
	Topi Miettinen <toiwoton@gmail.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v3 1/2] aarch64: align address for BTI protection [BZ #26988]
Date: Wed,  2 Dec 2020 08:55:14 +0000	[thread overview]
Message-ID: <d460a4f7aa4d70cc205f08896ed50b31fcd992df.1606898457.git.szabolcs.nagy@arm.com> (raw)
In-Reply-To: <ebce134991eae4261bbb32572a2062d3ca56e674.1606319495.git.szabolcs.nagy@arm.com>

Handle unaligned executable load segments (the bfd linker is not
expected to produce such binaries, but other linkers may).

Computing the mapping bounds follows _dl_map_object_from_fd more
closely now.

Fixes bug 26988.
---
v3:
- split the last patch in two so this bug is fixed separately.
- pushed to nsz/btifix-v3 branch.

 sysdeps/aarch64/dl-bti.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/sysdeps/aarch64/dl-bti.c b/sysdeps/aarch64/dl-bti.c
index 8f4728adce..67d63c8a73 100644
--- a/sysdeps/aarch64/dl-bti.c
+++ b/sysdeps/aarch64/dl-bti.c
@@ -20,19 +20,22 @@
 #include <libintl.h>
 #include <ldsodefs.h>
 
-static int
+static void
 enable_bti (struct link_map *map, const char *program)
 {
+  const size_t pagesz = GLRO(dl_pagesize);
   const ElfW(Phdr) *phdr;
-  unsigned prot;
 
   for (phdr = map->l_phdr; phdr < &map->l_phdr[map->l_phnum]; ++phdr)
     if (phdr->p_type == PT_LOAD && (phdr->p_flags & PF_X))
       {
-	void *start = (void *) (phdr->p_vaddr + map->l_addr);
-	size_t len = phdr->p_memsz;
+	size_t vstart = ALIGN_DOWN (phdr->p_vaddr, pagesz);
+	size_t vend = ALIGN_UP (phdr->p_vaddr + phdr->p_filesz, pagesz);
+	off_t off = ALIGN_DOWN (phdr->p_offset, pagesz);
+	void *start = (void *) (vstart + map->l_addr);
+	size_t len = vend - vstart;
 
-	prot = PROT_EXEC | PROT_BTI;
+	unsigned prot = PROT_EXEC | PROT_BTI;
 	if (phdr->p_flags & PF_R)
 	  prot |= PROT_READ;
 	if (phdr->p_flags & PF_W)
@@ -48,7 +51,6 @@ enable_bti (struct link_map *map, const char *program)
 				N_("mprotect failed to turn on BTI"));
 	  }
       }
-  return 0;
 }
 
 /* Enable BTI for MAP and its dependencies.  */
-- 
2.17.1

