From 2629b7e2cd8975f02a159db461d2460b9275545e Mon Sep 17 00:00:00 2001 From: Michael Brown Date: Mon, 11 Mar 2013 00:50:52 +0000 Subject: [PATCH] [pcbios] Inhibit all calls to INT 15,e820 and INT 15,e801 during POST Many BIOSes do not construct the full system memory map until after calling the option ROM initialisation entry points. For several years, we have added sanity checks and workarounds to accommodate charming quirks such as BIOSes which report the entire 32-bit address space (including all memory-mapped PCI BARs) as being usable RAM. The IBM x3650 takes quirky behaviour to a new extreme. Calling either INT 15,e820 or INT 15,e801 during POST doesn't just get you invalid data. We could cope with invalid data. Instead, these nominally read-only API calls manage to trash some internal BIOS state, with the result that the system memory map is _never_ constructed. This tends to confuse subsequent bootloaders and operating systems. [ GRUB 0.97 fails in a particularly amusing way. Someone thought it would be a good idea for memcpy() to check that the destination memory region is a valid part of the system memory map; if not, then memcpy() will sulk, fail, and return NULL. This breaks pretty much every use of memcpy() including, for example, those inserted implicitly by gcc to copy non-const initialisers. Debugging is _fun_ when a simple call to printf() manages to create an infinite recursion, exhaust the available stack space, and shut down the CPU. ] Fix by completely inhibiting calls to INT 15,e820 and INT 15,e801 during POST. We do now allow relocation during POST up to the maximum address returned by INT 15,88 (which seems so far to always be safe). This allows us to continue to have a reasonable size of external heap, even if the PMM allocation is close to the 1MB mark. The downside of allowing relocation during POST is that we may overwrite PMM-allocated memory in use by other option ROMs. However, the downside of inhibiting relocation, when combined with also inhibiting calls to INT 15,e820 and INT 15,e801, would be that we might have no external heap available: this would make booting an OS impossible and could prevent some devices from even completing initialisation. On balance, the lesser evil is probably to allow relocation during POST (up to the limit provided by INT 15,88). Entering iPXE during POST is a rare operation; on the even rarer systems where doing so happens to overwrite a PMM-allocated region, then there exists a fairly simple workaround: if the user enters iPXE during POST and wishes to exit iPXE, then the user must reboot. This is an acceptable cost, given the rarity of the situation and the simplicity of the workaround. Signed-off-by: Michael Brown --- src/arch/i386/core/relocate.c | 8 +++++--- src/arch/i386/firmware/pcbios/memmap.c | 16 ++++++++++++++++ src/arch/i386/prefix/exeprefix.S | 2 +- src/arch/i386/prefix/libprefix.S | 13 +++++++++++-- src/arch/i386/prefix/romprefix.S | 6 +++--- src/arch/i386/prefix/undiloader.S | 2 +- 6 files changed, 37 insertions(+), 10 deletions(-) diff --git a/src/arch/i386/core/relocate.c b/src/arch/i386/core/relocate.c index b9b02944..5fbf2d2c 100644 --- a/src/arch/i386/core/relocate.c +++ b/src/arch/i386/core/relocate.c @@ -33,8 +33,10 @@ extern char _etextdata[]; /** * Relocate iPXE * - * @v ix86 x86 register dump from prefix - * @ret ix86 x86 registers to return to prefix + * @v ebp Maximum address to use for relocation + * @ret esi Current physical address + * @ret edi New physical address + * @ret ecx Length to copy * * This finds a suitable location for iPXE near the top of 32-bit * address space, and returns the physical address of the new location @@ -59,7 +61,7 @@ __asmcall void relocate ( struct i386_all_regs *ix86 ) { /* Determine maximum usable address */ max = MAX_ADDR; - if ( ix86->regs.ebp && ( ix86->regs.ebp < max ) ) { + if ( ix86->regs.ebp < max ) { max = ix86->regs.ebp; DBG ( "Limiting relocation to [0,%lx)\n", max ); } diff --git a/src/arch/i386/firmware/pcbios/memmap.c b/src/arch/i386/firmware/pcbios/memmap.c index cf659226..0937a7ce 100644 --- a/src/arch/i386/firmware/pcbios/memmap.c +++ b/src/arch/i386/firmware/pcbios/memmap.c @@ -63,6 +63,10 @@ struct e820_entry { static struct e820_entry __bss16 ( e820buf ); #define e820buf __use_data16 ( e820buf ) +/** We are running during POST; inhibit INT 15,e820 and INT 15,e801 */ +uint8_t __bss16 ( memmap_post ); +#define memmap_post __use_data16 ( memmap_post ) + /** * Get size of extended memory via INT 15,e801 * @@ -74,6 +78,12 @@ static unsigned int extmemsize_e801 ( void ) { unsigned int flags; unsigned int extmem; + /* Inhibit INT 15,e801 during POST */ + if ( memmap_post ) { + DBG ( "INT 15,e801 not available during POST\n" ); + return 0; + } + __asm__ __volatile__ ( REAL_CODE ( "stc\n\t" "int $0x15\n\t" "pushfw\n\t" @@ -164,6 +174,12 @@ static int meme820 ( struct memory_map *memmap ) { unsigned int flags; unsigned int discard_D; + /* Inhibit INT 15,e820 during POST */ + if ( memmap_post ) { + DBG ( "INT 15,e820 not available during POST\n" ); + return -ENOTTY; + } + /* Clear the E820 buffer. Do this once before starting, * rather than on each call; some BIOSes rely on the contents * being preserved between calls. diff --git a/src/arch/i386/prefix/exeprefix.S b/src/arch/i386/prefix/exeprefix.S index acd3f83c..cb61287d 100644 --- a/src/arch/i386/prefix/exeprefix.S +++ b/src/arch/i386/prefix/exeprefix.S @@ -114,7 +114,7 @@ _exe_start: call alloc_basemem xorl %esi, %esi movl $EXE_DECOMPRESS_ADDRESS, %edi - xorl %ebp, %ebp + orl $0xffffffff, %ebp /* Allow arbitrary relocation */ call install_prealloc /* Set up real-mode stack */ diff --git a/src/arch/i386/prefix/libprefix.S b/src/arch/i386/prefix/libprefix.S index 0bd80b0a..197a86bc 100644 --- a/src/arch/i386/prefix/libprefix.S +++ b/src/arch/i386/prefix/libprefix.S @@ -622,7 +622,7 @@ install: /* Image destination = default */ xorl %edi, %edi /* Allow arbitrary relocation */ - xorl %ebp, %ebp + orl $0xffffffff, %ebp /* Install text and data segments */ call install_prealloc /* Restore registers and return */ @@ -642,7 +642,9 @@ install: * %bx : .data16 segment address * %esi : Image source physical address (or zero for %cs:0000) * %edi : Decompression temporary area physical address (or zero for default) - * %ebp : Maximum end address for relocation (or zero for no maximum) + * %ebp : Maximum end address for relocation + * - 0xffffffff for no maximum + * - 0x00000000 to inhibit use of INT 15,e820 and INT 15,e801 * Corrupts: * none **************************************************************************** @@ -796,6 +798,13 @@ payload_death_message: movw %ax, (init_librm_vector+2) lcall *init_librm_vector + /* Inhibit INT 15,e820 and INT 15,e801 if applicable */ + testl %ebp, %ebp + jnz 1f + incb memmap_post + decl %ebp +1: + /* Call relocate() to determine target address for relocation. * relocate() will return with %esi, %edi and %ecx set up * ready for the copy to the new location. diff --git a/src/arch/i386/prefix/romprefix.S b/src/arch/i386/prefix/romprefix.S index 35d037ef..18fef75e 100644 --- a/src/arch/i386/prefix/romprefix.S +++ b/src/arch/i386/prefix/romprefix.S @@ -445,7 +445,7 @@ no_pmm: * picked up by the initial shell prompt, and we will drop * into a shell. */ - movl $0xa0000, %ebp /* Inhibit relocation during POST */ + xorl %ebp, %ebp /* Inhibit use of INT 15,e820 and INT 15,e801 */ pushw %cs call exec 2: @@ -630,7 +630,7 @@ decompress_to: * Called by the PnP BIOS when it wants to boot us. */ bev_entry: - xorl %ebp, %ebp /* Allow relocation */ + orl $0xffffffff, %ebp /* Allow arbitrary relocation */ pushw %cs call exec lret @@ -665,7 +665,7 @@ int19_entry: /* Leave keypress in buffer and start iPXE. The keypress will * cause the usual initial Ctrl-B prompt to be skipped. */ - xorl %ebp, %ebp /* Allow relocation */ + orl $0xffffffff, %ebp /* Allow arbitrary relocation */ pushw %cs call exec 1: /* Try to call original INT 19 vector */ diff --git a/src/arch/i386/prefix/undiloader.S b/src/arch/i386/prefix/undiloader.S index bb3d469b..ccdd816e 100644 --- a/src/arch/i386/prefix/undiloader.S +++ b/src/arch/i386/prefix/undiloader.S @@ -31,7 +31,7 @@ undiloader: movw %es:14(%di), %ax movl image_source, %esi movl decompress_to, %edi - xorl %ebp, %ebp /* Allow relocation */ + orl $0xffffffff, %ebp /* Allow arbitrary relocation */ call install_prealloc popw %di /* Call UNDI loader C code */