[pcbios] Allow for larger-than-20-byte buffers in e820mangler.S

Although the E820 API allows for a caller to provide only a 20-byte
buffer, there exists at least one combination (HP BIOS, 32-bit WinPE)
that relies on information found only in the "extended attributes"
field, which requires a 24-byte buffer.

Allow for up to a 64-byte E820 buffer, in the hope of coping with
future idiocies like this one.

diff --git a/src/arch/i386/firmware/pcbios/e820mangler.S b/src/arch/i386/firmware/pcbios/e820mangler.S
index 437efa7..4fbd656 100644 (file)
--- a/src/arch/i386/firmware/pcbios/e820mangler.S
+++ b/src/arch/i386/firmware/pcbios/e820mangler.S
@@ -25,6 +25,26 @@
 
 #define SMAP 0x534d4150
 
 
 #define SMAP 0x534d4150
 

+/* Most documentation refers to the E820 buffer as being 20 bytes, and
+ * the API makes it perfectly legitimate to pass only a 20-byte buffer
+ * and expect to get valid data.  However, some morons at ACPI decided
+ * to extend the data structure by adding an extra "extended
+ * attributes" field and by including critical information within this
+ * field, such as whether or not the region is enabled.  A caller who
+ * passes in only a 20-byte buffer therefore risks getting very, very
+ * misleading information.
+ *
+ * I have personally witnessed an HP BIOS that returns a value of
+ * 0x0009 in the extended attributes field.  If we don't pass this
+ * value through to the caller, 32-bit WinPE will die, usually with a
+ * PAGE_FAULT_IN_NONPAGED_AREA blue screen of death.
+ *
+ * Allow a ridiculously large maximum value (64 bytes) for the E820
+ * buffer as a guard against insufficiently creative idiots in the
+ * future.
+ */
+#define E820MAXSIZE    64
+

 /****************************************************************************
  *
  * Allowed memory windows
 /****************************************************************************
  *
  * Allowed memory windows


@@ -204,19 +224,22 @@ get_underlying_e820:
 
        /* If the requested region is in the cache, return it */
        cmpw    %bx, underlying_e820_index
 
        /* If the requested region is in the cache, return it */
        cmpw    %bx, underlying_e820_index

-       jne     1f
+       jne     2f

        pushw   %di
        pushw   %si
        movw    $underlying_e820_cache, %si
        pushw   %di
        pushw   %si
        movw    $underlying_e820_cache, %si

-       movw    $20, %cx
+       cmpl    underlying_e820_cache_size, %ecx
+       jbe     1f
+       movl    underlying_e820_cache_size, %ecx
+1:     pushl   %ecx

        rep movsb
        rep movsb

+       popl    %ecx

        popw    %si
        popw    %di
        popw    %si
        popw    %di

-       movw    $20, %cx

        incw    %bx
        movl    %edx, %eax
        ret
        incw    %bx
        movl    %edx, %eax
        ret

-1:     
+2:     

        /* If the requested region is earlier than the cached region,
         * invalidate the cache.
         */
        /* If the requested region is earlier than the cached region,
         * invalidate the cache.
         */


@@ -250,23 +273,26 @@ get_underlying_e820:
        pushw   %ds
        popw    %es
        movw    $underlying_e820_cache, %di
        pushw   %ds
        popw    %es
        movw    $underlying_e820_cache, %di

-       movl    $20, %ecx
-       movl    underlying_e820_ebx, %ebx
+       cmpl    $E820MAXSIZE, %ecx
+       jbe     1f
+       movl    $E820MAXSIZE, %ecx
+1:     movl    underlying_e820_ebx, %ebx

        stc
        pushfw
        lcall   *%cs:int15_vector
        popw    %di
        popw    %es
        /* Check for error return from underlying e820 call */
        stc
        pushfw
        lcall   *%cs:int15_vector
        popw    %di
        popw    %es
        /* Check for error return from underlying e820 call */

-       jc      1f /* CF set: error */
+       jc      2f /* CF set: error */

        cmpl    $SMAP, %eax
        cmpl    $SMAP, %eax

-       je      2f /* 'SMAP' missing: error */
-1:     /* An error occurred: return values returned by underlying e820 call */
+       je      3f /* 'SMAP' missing: error */
+2:     /* An error occurred: return values returned by underlying e820 call */

        stc     /* Force CF set if SMAP was missing */
        addr32 leal 16(%esp), %esp /* avoid changing other flags */
        ret
        stc     /* Force CF set if SMAP was missing */
        addr32 leal 16(%esp), %esp /* avoid changing other flags */
        ret

-2:     /* No error occurred */
+3:     /* No error occurred */

        movl    %ebx, underlying_e820_ebx
        movl    %ebx, underlying_e820_ebx

+       movl    %ecx, underlying_e820_cache_size

        popl    %edx
        popl    %ecx
        popl    %ebx
        popl    %edx
        popl    %ecx
        popl    %ebx


@@ -290,9 +316,14 @@ underlying_e820_ebx:
 
        .section ".bss16"
 underlying_e820_cache:
 
        .section ".bss16"
 underlying_e820_cache:

-       .space  20
+       .space  E820MAXSIZE

        .size underlying_e820_cache, . - underlying_e820_cache
 
        .size underlying_e820_cache, . - underlying_e820_cache
 

+       .section ".bss16"
+underlying_e820_cache_size:
+       .long   0
+       .size   underlying_e820_cache_size, . - underlying_e820_cache_size
+

 /****************************************************************************
  * Get windowed e820 region, without empty region stripping
  *
 /****************************************************************************
  * Get windowed e820 region, without empty region stripping
  *


@@ -437,15 +468,15 @@ get_mangled_e820:
        /* Peek ahead to see if there are any further nonempty regions */
        pushal
        pushw   %es
        /* Peek ahead to see if there are any further nonempty regions */
        pushal
        pushw   %es

-       subw    $20, %sp
+       movw    %sp, %bp
+       subw    %cx, %sp

        movl    $0xe820, %eax
        movl    $SMAP, %edx
        movl    $0xe820, %eax
        movl    $SMAP, %edx

-       movl    $20, %ecx

        pushw   %ss
        popw    %es
        movw    %sp, %di
        call    get_nonempty_e820
        pushw   %ss
        popw    %es
        movw    %sp, %di
        call    get_nonempty_e820

-       addr32 leal 20(%esp), %esp /* avoid changing flags */
+       movw    %bp, %sp

        popw    %es
        popal
        jnc     99f /* There are further nonempty regions */
        popw    %es
        popal
        jnc     99f /* There are further nonempty regions */