git: 670af174e27b - main - arm64: Enable BTI in the kernel ELF loader

The branch main has been updated by andrew:

URL: https://cgit.FreeBSD.org/src/commit/?id=670af174e27b4f42f6e17521f18508ec78d5a776

commit 670af174e27b4f42f6e17521f18508ec78d5a776
Author:     Andrew Turner <andrew@FreeBSD.org>
AuthorDate: 2023-11-02 09:56:09 +0000
Commit:     Andrew Turner <andrew@FreeBSD.org>
CommitDate: 2024-02-22 16:27:47 +0000

    arm64: Enable BTI in the kernel ELF loader
    
    Enable BTI in binaries loaded by the kernel. When the ELF file contains
    the needed note indicating BTI is supported set the guarded page flag
    for all segments.
    
    Reviewed by:    markj
    Sponsored by:   Arm Ltd
    Differential Revision:  https://reviews.freebsd.org/D42441
---
 sys/arm64/arm64/elf_machdep.c | 73 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/sys/arm64/arm64/elf_machdep.c b/sys/arm64/arm64/elf_machdep.c
index 29427d04ee54..350651c42723 100644
--- a/sys/arm64/arm64/elf_machdep.c
+++ b/sys/arm64/arm64/elf_machdep.c
@@ -46,7 +46,9 @@
 #include <sys/vnode.h>
 
 #include <vm/vm.h>
+#include <vm/pmap.h>
 #include <vm/vm_param.h>
+#include <vm/vm_map.h>
 
 #include <machine/elf.h>
 #include <machine/md_var.h>
@@ -61,6 +63,8 @@ u_long __read_frequently linux_elf_hwcap2;
 
 struct arm64_addr_mask elf64_addr_mask;
 
+static void arm64_exec_protect(struct image_params *, int);
+
 static struct sysentvec elf64_freebsd_sysvec = {
 	.sv_size	= SYS_MAXSYSCALL,
 	.sv_table	= sysent,
@@ -98,6 +102,7 @@ static struct sysentvec elf64_freebsd_sysvec = {
 	.sv_hwcap	= &elf_hwcap,
 	.sv_hwcap2	= &elf_hwcap2,
 	.sv_onexec_old	= exec_onexec_old,
+	.sv_protect	= arm64_exec_protect,
 	.sv_onexit	= exit_onexit,
 	.sv_regset_begin = SET_BEGIN(__elfN(regset)),
 	.sv_regset_end	= SET_LIMIT(__elfN(regset)),
@@ -311,3 +316,71 @@ elf_cpu_parse_dynamic(caddr_t loadbase __unused, Elf_Dyn *dynamic __unused)
 
 	return (0);
 }
+
+static Elf_Note gnu_property_note = {
+	.n_namesz = sizeof(GNU_ABI_VENDOR),
+	.n_descsz = 16,
+	.n_type = NT_GNU_PROPERTY_TYPE_0,
+};
+
+static bool
+gnu_property_cb(const Elf_Note *note, void *arg0, bool *res)
+{
+	const uint32_t *data;
+	uintptr_t p;
+
+	*res = false;
+	p = (uintptr_t)(note + 1);
+	p += roundup2(note->n_namesz, 4);
+	data = (const uint32_t *)p;
+	if (data[0] != GNU_PROPERTY_AARCH64_FEATURE_1_AND)
+		return (false);
+	/*
+	 * The data length should be at least the size of a uint32, and be
+	 * a multiple of uint32_t's
+	 */
+	if (data[1] < sizeof(uint32_t) || (data[1] % sizeof(uint32_t)) != 0)
+		return (false);
+	if ((data[2] & GNU_PROPERTY_AARCH64_FEATURE_1_BTI) != 0)
+		*res = true;
+
+	return (true);
+}
+
+static void
+arm64_exec_protect(struct image_params *imgp, int flags __unused)
+{
+	const Elf_Ehdr *hdr;
+	const Elf_Phdr *phdr;
+	vm_offset_t sva, eva;
+	int i;
+	bool found;
+
+	/* Skip if BTI is not supported */
+	if ((elf_hwcap2 & HWCAP2_BTI) == 0)
+		return;
+
+	hdr = (const Elf_Ehdr *)imgp->image_header;
+	phdr = (const Elf_Phdr *)(imgp->image_header + hdr->e_phoff);
+
+	found = false;
+	for (i = 0; i < hdr->e_phnum; i++) {
+		if (phdr[i].p_type == PT_NOTE && __elfN(parse_notes)(imgp,
+		    &gnu_property_note, GNU_ABI_VENDOR, &phdr[i],
+		    gnu_property_cb, NULL)) {
+			found = true;
+			break;
+		}
+	}
+	if (!found)
+		return;
+
+	for (i = 0; i < hdr->e_phnum; i++) {
+		if (phdr[i].p_type != PT_LOAD || phdr[i].p_memsz == 0)
+			continue;
+
+		sva = phdr[i].p_vaddr + imgp->et_dyn_addr;
+		eva = sva + phdr[i].p_memsz;
+		pmap_bti_set(vmspace_pmap(imgp->proc->p_vmspace), sva, eva);
+	}
+}