From 53cc72da90f5b5a76b024b47fe4e38a81b495eb4 Mon Sep 17 00:00:00 2001
From: Michael Pratt <mpratt@google.com>
Date: Tue, 1 Oct 2019 11:29:35 -0700
Subject: Honor X bit on extra anon pages in PT_LOAD segments

Linux changed this behavior in 16e72e9b30986ee15f17fbb68189ca842c32af58
(v4.11). Previously, extra pages were always mapped RW. Now, those pages will
be executable if the segment specified PF_X. They still must be writeable.

PiperOrigin-RevId: 272256280
---
 pkg/sentry/loader/elf.go | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

(limited to 'pkg/sentry/loader')

diff --git a/pkg/sentry/loader/elf.go b/pkg/sentry/loader/elf.go
index ba9c9ce12..2d9251e92 100644
--- a/pkg/sentry/loader/elf.go
+++ b/pkg/sentry/loader/elf.go
@@ -323,18 +323,22 @@ func mapSegment(ctx context.Context, m *mm.MemoryManager, f *fs.File, phdr *elf.
 			return syserror.ENOEXEC
 		}
 
+		// N.B. Linux uses vm_brk_flags to map these pages, which only
+		// honors the X bit, always mapping at least RW. ignoring These
+		// pages are not included in the final brk region.
+		prot := usermem.ReadWrite
+		if phdr.Flags&elf.PF_X == elf.PF_X {
+			prot.Execute = true
+		}
+
 		if _, err := m.MMap(ctx, memmap.MMapOpts{
 			Length: uint64(anonSize),
 			Addr:   anonAddr,
 			// Fixed without Unmap will fail the mmap if something is
 			// already at addr.
-			Fixed:   true,
-			Private: true,
-			// N.B. Linux uses vm_brk to map these pages, ignoring
-			// the segment protections, instead always mapping RW.
-			// These pages are not included in the final brk
-			// region.
-			Perms:    usermem.ReadWrite,
+			Fixed:    true,
+			Private:  true,
+			Perms:    prot,
 			MaxPerms: usermem.AnyAccess,
 		}); err != nil {
 			ctx.Infof("Error mapping PT_LOAD segment %v anonymous memory: %v", phdr, err)
-- 
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