From: Roger Pau Monne Date: Wed, 17 Jan 2018 12:00:41 +0000 (+0000) Subject: xen/pvh: place the trampoline at page 0x1 X-Git-Tag: 4.10.0-shim-comet-3^0 X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=fa23f2aaa24c603f748b49b32378b738d18cc68f;p=people%2Fdariof%2Fxen.git xen/pvh: place the trampoline at page 0x1 Since PVH guest jump straight into trampoline_setup trampoline_phys is not initialized, thus the trampoline is relocated to address 0. This works, but has the undesirable effect of having VA 0 mapped to MFN 0, which means NULL pointed dereferences no longer trigger a page fault. In order to solve this, place the trampoline at page 0x1 and reserve the memory used by it. Signed-off-by: Roger Pau Monné Reviewed-by: Wei Liu --- diff --git a/xen/arch/x86/boot/head.S b/xen/arch/x86/boot/head.S index 14caca6798..c527910478 100644 --- a/xen/arch/x86/boot/head.S +++ b/xen/arch/x86/boot/head.S @@ -411,6 +411,9 @@ __pvh_start: /* Skip bootloader setup and bios setup, go straight to trampoline */ movb $1, sym_esi(pvh_boot) movb $1, sym_esi(skip_realmode) + + /* Set trampoline_phys to use mfn 1 to avoid having a mapping at VA 0 */ + movw $0x1000, sym_esi(trampoline_phys) jmp trampoline_setup #endif /* CONFIG_PVH_GUEST */ diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 371c764027..a8b59617d3 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -292,9 +292,14 @@ void __init arch_init_memory(void) /* * First 1MB of RAM is historically marked as I/O. If we booted PVH, * reclaim the space. Irrespective, leave MFN 0 as special for the sake - * of 0 being a very common default value. + * of 0 being a very common default value. Also reserve page 0x1 which is + * used by the trampoline code on PVH. */ - for ( i = 0; i < (pvh_boot ? 1 : 0x100); i++ ) + BUG_ON(pvh_boot && trampoline_phys != 0x1000); + for ( i = 0; + i < (pvh_boot ? (1 + PFN_UP(trampoline_end - trampoline_start)) + : 0x100); + i++ ) share_xen_page_with_guest(mfn_to_page(_mfn(i)), dom_io, XENSHARE_writable);