s390/boot: Rework deployment of the kernel image

Rework deployment of kernel image for both compressed and
uncompressed variants as defined by CONFIG_KERNEL_UNCOMPRESSED
kernel configuration variable.

In case CONFIG_KERNEL_UNCOMPRESSED is disabled avoid uncompressing
the kernel to a temporary buffer and copying it to the target
address. Instead, uncompress it directly to the target destination.

In case CONFIG_KERNEL_UNCOMPRESSED is enabled avoid moving the
kernel to default 0x100000 location when KASLR is disabled or
failed. Instead, use the uncompressed kernel image directly.

In case KASLR is disabled or failed .amode31 section location in
memory is not randomized and precedes the kernel image. In case
CONFIG_KERNEL_UNCOMPRESSED is disabled that location overlaps the
area used by the decompression algorithm. That is fine, since that
area is not used after the decompression finished and the size of
.amode31 section is not expected to exceed BOOT_HEAP_SIZE ever.

There is no decompression in case CONFIG_KERNEL_UNCOMPRESSED is
enabled. Therefore, rename decompress_kernel() to deploy_kernel(),
which better describes both uncompressed and compressed cases.

Introduce AMODE31_SIZE macro to avoid immediate value of 0x3000
(the size of .amode31 section) in the decompressor linker script.
Modify the vmlinux linker script to force the size of .amode31
section to AMODE31_SIZE (the value of (_eamode31 - _samode31)
could otherwise differ as result of compiler options used).

Introduce __START_KERNEL macro that defines the kernel ELF image
entry point and set it to the currrent value of 0x100000.

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

1 files changed, 47 insertions, 43 deletions

diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index fc9c1d51ef8d..949eff7107cc 100644
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -109,9 +109,19 @@ static void setup_lpp(void)
 }
 
 #ifdef CONFIG_KERNEL_UNCOMPRESSED
-unsigned long mem_safe_offset(void)
+static unsigned long mem_safe_offset(void)
 {
-	return vmlinux.default_lma + vmlinux.image_size + vmlinux.bss_size;
+	return (unsigned long)_compressed_start;
+}
+
+static void deploy_kernel(void *output)
+{
+	void *uncompressed_start = (void *)_compressed_start;
+
+	if (output == uncompressed_start)
+		return;
+	memmove(output, uncompressed_start, vmlinux.image_size);
+	memset(uncompressed_start, 0, vmlinux.image_size);
 }
 #endif
 
@@ -154,18 +164,18 @@ static void kaslr_adjust_relocs(unsigned long min_addr, unsigned long max_addr,
 	rela_end = (Elf64_Rela *) vmlinux.rela_dyn_end;
 	dynsym = (Elf64_Sym *) vmlinux.dynsym_start;
 	for (rela = rela_start; rela < rela_end; rela++) {
-		loc = rela->r_offset + phys_offset;
+		loc = rela->r_offset + phys_offset - __START_KERNEL;
 		val = rela->r_addend;
 		r_sym = ELF64_R_SYM(rela->r_info);
 		if (r_sym) {
 			if (dynsym[r_sym].st_shndx != SHN_UNDEF)
-				val += dynsym[r_sym].st_value + offset;
+				val += dynsym[r_sym].st_value + offset - __START_KERNEL;
 		} else {
 			/*
-			 * 0 == undefined symbol table index (STN_UNDEF),
+			 * 0 == undefined symbol table index (SHN_UNDEF),
 			 * used for R_390_RELATIVE, only add KASLR offset
 			 */
-			val += offset;
+			val += offset - __START_KERNEL;
 		}
 		r_type = ELF64_R_TYPE(rela->r_info);
 		rc = arch_kexec_do_relocs(r_type, (void *) loc, val, 0);
@@ -206,7 +216,7 @@ static void kaslr_adjust_relocs(unsigned long min_addr, unsigned long max_addr,
 		loc = (long)*reloc + phys_offset;
 		if (loc < min_addr || loc > max_addr)
 			error("64-bit relocation outside of kernel!\n");
-		*(u64 *)loc += offset;
+		*(u64 *)loc += offset - __START_KERNEL;
 	}
 }
 
@@ -219,7 +229,7 @@ static void kaslr_adjust_got(unsigned long offset)
 	 * reason. Adjust the GOT entries.
 	 */
 	for (entry = (u64 *)vmlinux.got_start; entry < (u64 *)vmlinux.got_end; entry++)
-		*entry += offset;
+		*entry += offset - __START_KERNEL;
 }
 #endif
 
@@ -294,6 +304,7 @@ static unsigned long setup_kernel_memory_layout(unsigned long kernel_size)
 	vmemmap_size = SECTION_ALIGN_UP(pages) * sizeof(struct page);
 
 	/* choose kernel address space layout: 4 or 3 levels. */
+	BUILD_BUG_ON(!IS_ALIGNED(__START_KERNEL, THREAD_SIZE));
 	BUILD_BUG_ON(!IS_ALIGNED(__NO_KASLR_START_KERNEL, THREAD_SIZE));
 	BUILD_BUG_ON(__NO_KASLR_END_KERNEL > _REGION1_SIZE);
 	vsize = get_vmem_size(ident_map_size, vmemmap_size, vmalloc_size, _REGION3_SIZE);
@@ -383,9 +394,9 @@ static unsigned long setup_kernel_memory_layout(unsigned long kernel_size)
 /*
  * This function clears the BSS section of the decompressed Linux kernel and NOT the decompressor's.
  */
-static void clear_bss_section(unsigned long vmlinux_lma)
+static void clear_bss_section(unsigned long kernel_start)
 {
-	memset((void *)vmlinux_lma + vmlinux.image_size, 0, vmlinux.bss_size);
+	memset((void *)kernel_start + vmlinux.image_size, 0, vmlinux.bss_size);
 }
 
 /*
@@ -402,7 +413,7 @@ static void setup_vmalloc_size(void)
 	vmalloc_size = max(size, vmalloc_size);
 }
 
-static void kaslr_adjust_vmlinux_info(unsigned long offset)
+static void kaslr_adjust_vmlinux_info(long offset)
 {
 	vmlinux.bootdata_off += offset;
 	vmlinux.bootdata_preserved_off += offset;
@@ -426,24 +437,30 @@ static void kaslr_adjust_vmlinux_info(unsigned long offset)
 #endif
 }
 
+static void fixup_vmlinux_info(void)
+{
+	vmlinux.entry -= __START_KERNEL;
+	kaslr_adjust_vmlinux_info(-__START_KERNEL);
+}
+
 void startup_kernel(void)
 {
-	unsigned long max_physmem_end;
-	unsigned long vmlinux_lma = 0;
+	unsigned long kernel_size = vmlinux.image_size + vmlinux.bss_size;
+	unsigned long nokaslr_offset_phys = mem_safe_offset();
 	unsigned long amode31_lma = 0;
-	unsigned long kernel_size;
+	unsigned long max_physmem_end;
 	unsigned long asce_limit;
 	unsigned long safe_addr;
-	void *img;
 	psw_t psw;
 
+	fixup_vmlinux_info();
 	setup_lpp();
-	safe_addr = mem_safe_offset();
+	safe_addr = PAGE_ALIGN(nokaslr_offset_phys + kernel_size);
 
 	/*
-	 * Reserve decompressor memory together with decompression heap, buffer and
-	 * memory which might be occupied by uncompressed kernel at default 1Mb
-	 * position (if KASLR is off or failed).
+	 * Reserve decompressor memory together with decompression heap,
+	 * buffer and memory which might be occupied by uncompressed kernel
+	 * (if KASLR is off or failed).
 	 */
 	physmem_reserve(RR_DECOMPRESSOR, 0, safe_addr);
 	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && parmarea.initrd_size)
@@ -463,7 +480,6 @@ void startup_kernel(void)
 	max_physmem_end = detect_max_physmem_end();
 	setup_ident_map_size(max_physmem_end);
 	setup_vmalloc_size();
-	kernel_size = vmlinux.default_lma + vmlinux.image_size + vmlinux.bss_size;
 	asce_limit = setup_kernel_memory_layout(kernel_size);
 	/* got final ident_map_size, physmem allocations could be performed now */
 	physmem_set_usable_limit(ident_map_size);
@@ -472,32 +488,20 @@ void startup_kernel(void)
 	rescue_initrd(safe_addr, ident_map_size);
 	rescue_relocs();
 
-	if (kaslr_enabled()) {
-		vmlinux_lma = randomize_within_range(vmlinux.image_size + vmlinux.bss_size,
-						     THREAD_SIZE, vmlinux.default_lma,
-						     ident_map_size);
-		if (vmlinux_lma) {
-			__kaslr_offset_phys = vmlinux_lma - vmlinux.default_lma;
-			kaslr_adjust_vmlinux_info(__kaslr_offset_phys);
-		}
-	}
-	vmlinux_lma = vmlinux_lma ?: vmlinux.default_lma;
-	physmem_reserve(RR_VMLINUX, vmlinux_lma, vmlinux.image_size + vmlinux.bss_size);
-
-	if (!IS_ENABLED(CONFIG_KERNEL_UNCOMPRESSED)) {
-		img = decompress_kernel();
-		memmove((void *)vmlinux_lma, img, vmlinux.image_size);
-	} else if (__kaslr_offset_phys) {
-		img = (void *)vmlinux.default_lma;
-		memmove((void *)vmlinux_lma, img, vmlinux.image_size);
-		memset(img, 0, vmlinux.image_size);
-	}
+	if (kaslr_enabled())
+		__kaslr_offset_phys = randomize_within_range(kernel_size, THREAD_SIZE, 0, ident_map_size);
+	if (!__kaslr_offset_phys)
+		__kaslr_offset_phys = nokaslr_offset_phys;
+	kaslr_adjust_vmlinux_info(__kaslr_offset_phys);
+	physmem_reserve(RR_VMLINUX, __kaslr_offset_phys, kernel_size);
+	deploy_kernel((void *)__kaslr_offset_phys);
 
 	/* vmlinux decompression is done, shrink reserved low memory */
 	physmem_reserve(RR_DECOMPRESSOR, 0, (unsigned long)_decompressor_end);
 	if (kaslr_enabled())
 		amode31_lma = randomize_within_range(vmlinux.amode31_size, PAGE_SIZE, 0, SZ_2G);
-	amode31_lma = amode31_lma ?: vmlinux.default_lma - vmlinux.amode31_size;
+	if (!amode31_lma)
+		amode31_lma = __kaslr_offset_phys - vmlinux.amode31_size;
 	physmem_reserve(RR_AMODE31, amode31_lma, vmlinux.amode31_size);
 
 	/*
@@ -513,8 +517,8 @@ void startup_kernel(void)
 	 * - copy_bootdata() must follow setup_vmem() to propagate changes
 	 *   to bootdata made by setup_vmem()
 	 */
-	clear_bss_section(vmlinux_lma);
-	kaslr_adjust_relocs(vmlinux_lma, vmlinux_lma + vmlinux.image_size,
+	clear_bss_section(__kaslr_offset_phys);
+	kaslr_adjust_relocs(__kaslr_offset_phys, __kaslr_offset_phys + vmlinux.image_size,
 			    __kaslr_offset, __kaslr_offset_phys);
 	kaslr_adjust_got(__kaslr_offset);
 	free_relocs();