[PATCH v9 4/5] linux-user: Parse NT_GNU_PROPERTY_TYPE_0 notes

[Richard Henderson]

For aarch64, this includes the GNU_PROPERTY_AARCH64_FEATURE_1_BTI bit,
which indicates that the image should be mapped with guarded pages.

Signed-off-by: Richard Henderson <address@hidden>
---
v9: Only map the startup executable with BTI; anything else must be
    handled by the interpreter.
---
 linux-user/qemu.h    |   4 ++
 linux-user/elfload.c | 143 ++++++++++++++++++++++++++++++++-----------
 2 files changed, 112 insertions(+), 35 deletions(-)

diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index ce902f5132..d36b18b678 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -61,6 +61,10 @@ struct image_info {
         abi_ulong       interpreter_loadmap_addr;
         abi_ulong       interpreter_pt_dynamic_addr;
         struct image_info *other_info;
+
+        /* For target-specific processing of NT_GNU_PROPERTY_TYPE_0. */
+        uint32_t        note_flags;
+
 #ifdef TARGET_MIPS
         int             fp_abi;
         int             interp_fp_abi;
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 01a9323a63..c84c9991fd 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2319,7 +2319,7 @@ static void load_elf_image(const char *image_name, int 
image_fd,
     struct elfhdr *ehdr = (struct elfhdr *)bprm_buf;
     struct elf_phdr *phdr;
     abi_ulong load_addr, load_bias, loaddr, hiaddr, error;
-    int i, retval;
+    int i, retval, prot_exec;
     const char *errmsg;
 
     /* First of all, some simple consistency checks */
@@ -2354,17 +2354,90 @@ static void load_elf_image(const char *image_name, int 
image_fd,
     loaddr = -1, hiaddr = 0;
     info->alignment = 0;
     for (i = 0; i < ehdr->e_phnum; ++i) {
-        if (phdr[i].p_type == PT_LOAD) {
-            abi_ulong a = phdr[i].p_vaddr - phdr[i].p_offset;
+        struct elf_phdr *eppnt = phdr + i;
+
+        if (eppnt->p_type == PT_LOAD) {
+            abi_ulong a = eppnt->p_vaddr - eppnt->p_offset;
             if (a < loaddr) {
                 loaddr = a;
             }
-            a = phdr[i].p_vaddr + phdr[i].p_memsz;
+            a = eppnt->p_vaddr + eppnt->p_memsz;
             if (a > hiaddr) {
                 hiaddr = a;
             }
             ++info->nsegs;
-            info->alignment |= phdr[i].p_align;
+            info->alignment |= eppnt->p_align;
+        } else if (eppnt->p_type == PT_INTERP && pinterp_name) {
+            char *interp_name;
+
+            if (*pinterp_name) {
+                errmsg = "Multiple PT_INTERP entries";
+                goto exit_errmsg;
+            }
+            interp_name = malloc(eppnt->p_filesz);
+            if (!interp_name) {
+                goto exit_perror;
+            }
+
+            if (eppnt->p_offset + eppnt->p_filesz <= BPRM_BUF_SIZE) {
+                memcpy(interp_name, bprm_buf + eppnt->p_offset,
+                       eppnt->p_filesz);
+            } else {
+                retval = pread(image_fd, interp_name, eppnt->p_filesz,
+                               eppnt->p_offset);
+                if (retval != eppnt->p_filesz) {
+                    goto exit_perror;
+                }
+            }
+            if (interp_name[eppnt->p_filesz - 1] != 0) {
+                errmsg = "Invalid PT_INTERP entry";
+                goto exit_errmsg;
+            }
+            *pinterp_name = interp_name;
+        } else if (eppnt->p_type == PT_GNU_PROPERTY) {
+            /* Process NT_GNU_PROPERTY_TYPE_0. */
+            const uint32_t gnu0_magic = const_le32('G' | 'N' << 8 | 'U' << 16);
+            uint32_t note[7];
+
+            /*
+             * The note contents are 7 words, but depending on LP64 vs ILP32
+             * there may be an 8th padding word at the end.  Check for and
+             * read the minimum size.  Further checks below will validate
+             * that the sizes of everything involved are as we expect.
+             */
+            if (eppnt->p_filesz < sizeof(note)) {
+                continue;
+            }
+            if (eppnt->p_offset + eppnt->p_filesz <= BPRM_BUF_SIZE) {
+                memcpy(note, bprm_buf + eppnt->p_offset, sizeof(note));
+            } else {
+                retval = pread(image_fd, note, sizeof(note), eppnt->p_offset);
+                if (retval != sizeof(note)) {
+                    goto exit_perror;
+                }
+            }
+#ifdef BSWAP_NEEDED
+            for (i = 0; i < ARRAY_SIZE(note); ++i) {
+                bswap32s(note + i);
+            }
+#endif
+            /*
+             * Check that this is a NT_GNU_PROPERTY_TYPE_0 note.
+             * Again, descsz includes padding.  Full size validation
+             * awaits checking the final payload.
+             */
+            if (note[0] != 4 ||                       /* namesz */
+                note[1] < 12 ||                       /* descsz */
+                note[2] != NT_GNU_PROPERTY_TYPE_0 ||  /* type */
+                note[3] != gnu0_magic) {              /* name */
+                continue;
+            }
+#ifdef TARGET_AARCH64
+            if (note[4] == GNU_PROPERTY_AARCH64_FEATURE_1_AND &&
+                note[5] == 4) {
+                info->note_flags = note[6];
+            }
+#endif /* TARGET_AARCH64 */
         }
     }
 
@@ -2453,15 +2526,42 @@ static void load_elf_image(const char *image_name, int 
image_fd,
     info->brk = 0;
     info->elf_flags = ehdr->e_flags;
 
+    prot_exec = PROT_EXEC;
+#ifdef TARGET_AARCH64
+    /*
+     * If the BTI feature is present, this indicates that the executable
+     * pages of the startup binary should be mapped with PROT_BTI, so that
+     * branch targets are enforced.
+     *
+     * The startup executable is either the interpreter or the static
+     * binary.  The interpreter is responsible for all pages of a
+     * dynamic executable.
+     *
+     * Elf notes are backward compatible to older cpus.
+     * Do not enable BTI unless it is supported.
+     */
+    if ((info->note_flags & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)
+        && (pinterp_name == NULL || *pinterp_name == 0)
+        && cpu_isar_feature(aa64_bti, ARM_CPU(thread_cpu))) {
+        prot_exec |= TARGET_PROT_BTI;
+    }
+#endif
+
     for (i = 0; i < ehdr->e_phnum; i++) {
         struct elf_phdr *eppnt = phdr + i;
         if (eppnt->p_type == PT_LOAD) {
             abi_ulong vaddr, vaddr_po, vaddr_ps, vaddr_ef, vaddr_em, vaddr_len;
             int elf_prot = 0;
 
-            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;
+            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 = load_bias + eppnt->p_vaddr;
             vaddr_po = TARGET_ELF_PAGEOFFSET(vaddr);
@@ -2511,33 +2611,6 @@ static void load_elf_image(const char *image_name, int 
image_fd,
                     info->brk = vaddr_em;
                 }
             }
-        } else if (eppnt->p_type == PT_INTERP && pinterp_name) {
-            char *interp_name;
-
-            if (*pinterp_name) {
-                errmsg = "Multiple PT_INTERP entries";
-                goto exit_errmsg;
-            }
-            interp_name = malloc(eppnt->p_filesz);
-            if (!interp_name) {
-                goto exit_perror;
-            }
-
-            if (eppnt->p_offset + eppnt->p_filesz <= BPRM_BUF_SIZE) {
-                memcpy(interp_name, bprm_buf + eppnt->p_offset,
-                       eppnt->p_filesz);
-            } else {
-                retval = pread(image_fd, interp_name, eppnt->p_filesz,
-                               eppnt->p_offset);
-                if (retval != eppnt->p_filesz) {
-                    goto exit_perror;
-                }
-            }
-            if (interp_name[eppnt->p_filesz - 1] != 0) {
-                errmsg = "Invalid PT_INTERP entry";
-                goto exit_errmsg;
-            }
-            *pinterp_name = interp_name;
 #ifdef TARGET_MIPS
         } else if (eppnt->p_type == PT_MIPS_ABIFLAGS) {
             Mips_elf_abiflags_v0 abiflags;
-- 
2.20.1