[PATCH 1/2] x86/setup: consolidate early memory reservations

Mike Rapoport
2021-01-15T08:33:28Z

From: Mike Rapoport <rppt@linux.ibm.com>

The early reservations of memory areas used by the firmware, bootloader,
kernel text and data are spread over setup_arch(). Moreover, some of them
happen *after* memblock allocations, e.g trim_platform_memory_ranges() and
trim_low_memory_range() are called after reserve_real_mode() that allocates
memory.

We did not observe corruption of these memory regions because memblock
always allocates memory either from the end of memory (in top-down mode) or
above the kernel image (in bottom-up mode). However, the bottom up mode is
going to be updated to span the entire memory [1] to avoid limitations
caused by KASLR.

Consolidate early memory reservations in a dedicated function to improve
robustness against future changes. Having the early reservations in one
place also makes it clearer what memory must be reserved before we allow
memblock allocations.

[1] https://lore.kernel.org/lkml/20201217201214.3414100-2-guro@fb.com

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
arch/x86/kernel/setup.c | 80 ++++++++++++++++++++++-------------------
1 file changed, 44 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3412c4595efd..32cd2e790a0a 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -728,7 +728,38 @@ static void __init trim_low_memory_range(void)
*/
memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
}
-
+
+static void __init early_reserve_memory(void)
+{
+ /*
+ * Reserve the memory occupied by the kernel between _text and
+ * __end_of_kernel_reserve symbols. Any kernel sections after the
+ * __end_of_kernel_reserve symbol must be explicitly reserved with a
+ * separate memblock_reserve() or they will be discarded.
+ */
+ memblock_reserve(__pa_symbol(_text),
+ (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
+
+ /*
+ * Make sure page 0 is always reserved because on systems with
+ * L1TF its contents can be leaked to user processes.
+ */
+ memblock_reserve(0, PAGE_SIZE);
+
+ early_reserve_initrd();
+
+ if (efi_enabled(EFI_BOOT))
+ efi_memblock_x86_reserve_range();
+
+ memblock_x86_reserve_range_setup_data();
+
+ reserve_ibft_region();
+ reserve_bios_regions();
+
+ trim_platform_memory_ranges();
+ trim_low_memory_range();
+}
+
/*
* Dump out kernel offset information on panic.
*/
@@ -763,29 +794,6 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)

void __init setup_arch(char **cmdline_p)
{
- /*
- * Reserve the memory occupied by the kernel between _text and
- * __end_of_kernel_reserve symbols. Any kernel sections after the
- * __end_of_kernel_reserve symbol must be explicitly reserved with a
- * separate memblock_reserve() or they will be discarded.
- */
- memblock_reserve(__pa_symbol(_text),
- (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
-
- /*
- * Make sure page 0 is always reserved because on systems with
- * L1TF its contents can be leaked to user processes.
- */
- memblock_reserve(0, PAGE_SIZE);
-
- early_reserve_initrd();
-
- /*
- * At this point everything still needed from the boot loader
- * or BIOS or kernel text should be early reserved or marked not
- * RAM in e820. All other memory is free game.
- */
-
#ifdef CONFIG_X86_32
memcpy(&boot_cpu_data, &new_cpu_data, sizeof(new_cpu_data));

@@ -909,8 +917,18 @@ void __init setup_arch(char **cmdline_p)

parse_early_param();

- if (efi_enabled(EFI_BOOT))
- efi_memblock_x86_reserve_range();
+ /*
+ * Do some memory reservations *before* memory is added to
+ * memblock, so memblock allocations won't overwrite it.
+ * Do it after early param, so we could get (unlikely) panic from
+ * serial.
+ *
+ * After this point everything still needed from the boot loader or
+ * firmware or kernel text should be early reserved or marked not
+ * RAM in e820. All other memory is free game.
+ */
+ early_reserve_memory();
+
#ifdef CONFIG_MEMORY_HOTPLUG
/*
* Memory used by the kernel cannot be hot-removed because Linux
@@ -937,9 +955,6 @@ void __init setup_arch(char **cmdline_p)

x86_report_nx();

- /* after early param, so could get panic from serial */
- memblock_x86_reserve_range_setup_data();
-
if (acpi_mps_check()) {
#ifdef CONFIG_X86_LOCAL_APIC
disable_apic = 1;
@@ -1031,8 +1046,6 @@ void __init setup_arch(char **cmdline_p)
*/
find_smp_config();

- reserve_ibft_region();
-
early_alloc_pgt_buf();

/*
@@ -1053,8 +1066,6 @@ void __init setup_arch(char **cmdline_p)
*/
sev_setup_arch();

- reserve_bios_regions();
-
efi_fake_memmap();
efi_find_mirror();
efi_esrt_init();
@@ -1080,9 +1091,6 @@ void __init setup_arch(char **cmdline_p)

reserve_real_mode();

- trim_platform_memory_ranges();
- trim_low_memory_range();
-
init_mem_mapping();

idt_setup_early_pf();
--
2.28.0