x86/boot/compressed/64: Validate trampoline placement against E820

There were two report of boot failure cased by trampoline placed into
a reserved memory region. It can happen on machines that don't report
EBDA correctly.

Fix the problem by re-validating the found address against the E820 table.
If the address is in a reserved area, find the next usable region below the
initial address.

Fixes: 3548e131ec6a ("x86/boot/compressed/64: Find a place for 32-bit trampoline")
Reported-by: Dmitry Malkin <d.malkin@real-time-systems.com>
Reported-by: youling 257 <youling257@gmail.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20180801133225.38121-1-kirill.shutemov@linux.intel.com

diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
index 8c51075..9e21573 100644 (file)
--- a/arch/x86/boot/compressed/pgtable_64.c
+++ b/arch/x86/boot/compressed/pgtable_64.c
@@ -1,3 +1,4 @@
+#include <asm/e820/types.h>
 #include <asm/processor.h>
 #include "pgtable.h"
 #include "../string.h"
@@ -34,10 +35,62 @@ unsigned long *trampoline_32bit __section(.data);
 extern struct boot_params *boot_params;
 int cmdline_find_option_bool(const char *option);
 
+static unsigned long find_trampoline_placement(void)
+{
+       unsigned long bios_start, ebda_start;
+       unsigned long trampoline_start;
+       struct boot_e820_entry *entry;
+       int i;
+
+       /*
+        * Find a suitable spot for the trampoline.
+        * This code is based on reserve_bios_regions().
+        */
+
+       ebda_start = *(unsigned short *)0x40e << 4;
+       bios_start = *(unsigned short *)0x413 << 10;
+
+       if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
+               bios_start = BIOS_START_MAX;
+
+       if (ebda_start > BIOS_START_MIN && ebda_start < bios_start)
+               bios_start = ebda_start;
+
+       bios_start = round_down(bios_start, PAGE_SIZE);
+
+       /* Find the first usable memory region under bios_start. */
+       for (i = boot_params->e820_entries - 1; i >= 0; i--) {
+               entry = &boot_params->e820_table[i];
+
+               /* Skip all entries above bios_start. */
+               if (bios_start <= entry->addr)
+                       continue;
+
+               /* Skip non-RAM entries. */
+               if (entry->type != E820_TYPE_RAM)
+                       continue;
+
+               /* Adjust bios_start to the end of the entry if needed. */
+               if (bios_start > entry->addr + entry->size)
+                       bios_start = entry->addr + entry->size;
+
+               /* Keep bios_start page-aligned. */
+               bios_start = round_down(bios_start, PAGE_SIZE);
+
+               /* Skip the entry if it's too small. */
+               if (bios_start - TRAMPOLINE_32BIT_SIZE < entry->addr)
+                       continue;
+
+               break;
+       }
+
+       /* Place the trampoline just below the end of low memory */
+       return bios_start - TRAMPOLINE_32BIT_SIZE;
+}
+
 struct paging_config paging_prepare(void *rmode)
 {
        struct paging_config paging_config = {};
-       unsigned long bios_start, ebda_start;
 
        /* Initialize boot_params. Required for cmdline_find_option_bool(). */
        boot_params = rmode;
@@ -61,23 +114,7 @@ struct paging_config paging_prepare(void *rmode)
                paging_config.l5_required = 1;
        }
 
-       /*
-        * Find a suitable spot for the trampoline.
-        * This code is based on reserve_bios_regions().
-        */
-
-       ebda_start = *(unsigned short *)0x40e << 4;
-       bios_start = *(unsigned short *)0x413 << 10;
-
-       if (bios_start < BIOS_START_MIN || bios_start > BIOS_START_MAX)
-               bios_start = BIOS_START_MAX;
-
-       if (ebda_start > BIOS_START_MIN && ebda_start < bios_start)
-               bios_start = ebda_start;
-
-       /* Place the trampoline just below the end of low memory, aligned to 4k */
-       paging_config.trampoline_start = bios_start - TRAMPOLINE_32BIT_SIZE;
-       paging_config.trampoline_start = round_down(paging_config.trampoline_start, PAGE_SIZE);
+       paging_config.trampoline_start = find_trampoline_placement();
 
        trampoline_32bit = (unsigned long *)paging_config.trampoline_start;