[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v1 07/13] xen/arm: Simplify alternative patching of non-writable region
On Tue, 5 Jun 2018, Julien Grall wrote: > During the MMU setup process, Xen will set SCTLR_EL2.WNX > (Write-Non-eXecutable) bit. Because of that, the alternative code need > to re-mapped the region in a difference place in order to modify the > text section. > > At the moment, the function patching the code is only aware of the > re-mapped region. This requires the caller to mess with Xen internal in > order to have function such as is_active_kernel_text() working. > > All the interaction with Xen internal can be removed by specify the ^ interactions ^ specifying > offset between the region patch and the writable region for updating the > instruction > > This simplification will also make easier to integrate dynamic patching ^ make it > a in a follow-up patch. Indeed, the callback address should be in ^ remove a > a original region and not re-mapped only which is writeable non-executable. ^ an > This is part of XSA-263. > > Signed-off-by: Julien Grall <julien.grall@xxxxxxx> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx> > --- > > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > > Changes in v2: > - Add commit message > - Remove comment in the code that does not make sense anymore > --- > xen/arch/arm/alternative.c | 42 +++++++++++++----------------------------- > 1 file changed, 13 insertions(+), 29 deletions(-) > > diff --git a/xen/arch/arm/alternative.c b/xen/arch/arm/alternative.c > index 9ffdc475d6..936cf04956 100644 > --- a/xen/arch/arm/alternative.c > +++ b/xen/arch/arm/alternative.c > @@ -97,12 +97,16 @@ static u32 get_alt_insn(const struct alt_instr *alt, > /* > * The region patched should be read-write to allow __apply_alternatives > * to replacing the instructions when necessary. > + * > + * @update_offset: Offset between the region patched and the writable > + * region for the update. 0 if the patched region is writable. > */ > -static int __apply_alternatives(const struct alt_region *region) > +static int __apply_alternatives(const struct alt_region *region, > + paddr_t update_offset) > { > const struct alt_instr *alt; > - const u32 *replptr; > - u32 *origptr; > + const u32 *replptr, *origptr; > + u32 *updptr; > > printk(XENLOG_INFO "alternatives: Patching with alt table %p -> %p\n", > region->begin, region->end); > @@ -118,6 +122,7 @@ static int __apply_alternatives(const struct alt_region > *region) > BUG_ON(alt->alt_len != alt->orig_len); > > origptr = ALT_ORIG_PTR(alt); > + updptr = (void *)origptr + update_offset; > replptr = ALT_REPL_PTR(alt); > > nr_inst = alt->alt_len / sizeof(insn); > @@ -125,7 +130,7 @@ static int __apply_alternatives(const struct alt_region > *region) > for ( i = 0; i < nr_inst; i++ ) > { > insn = get_alt_insn(alt, origptr + i, replptr + i); > - *(origptr + i) = cpu_to_le32(insn); > + *(updptr + i) = cpu_to_le32(insn); > } > > /* Ensure the new instructions reached the memory and nuke */ > @@ -162,9 +167,6 @@ static int __apply_alternatives_multi_stop(void *unused) > paddr_t xen_size = _end - _start; > unsigned int xen_order = get_order_from_bytes(xen_size); > void *xenmap; > - struct virtual_region patch_region = { > - .list = LIST_HEAD_INIT(patch_region.list), > - }; > > BUG_ON(patched); > > @@ -177,31 +179,13 @@ static int __apply_alternatives_multi_stop(void *unused) > /* Re-mapping Xen is not expected to fail during boot. */ > BUG_ON(!xenmap); > > - /* > - * If we generate a new branch instruction, the target will be > - * calculated in this re-mapped Xen region. So we have to register > - * this re-mapped Xen region as a virtual region temporarily. > - */ > - patch_region.start = xenmap; > - patch_region.end = xenmap + xen_size; > - register_virtual_region(&patch_region); > + region.begin = __alt_instructions; > + region.end = __alt_instructions_end; > > - /* > - * Find the virtual address of the alternative region in the new > - * mapping. > - * alt_instr contains relative offset, so the function > - * __apply_alternatives will patch in the re-mapped version of > - * Xen. > - */ > - region.begin = (void *)__alt_instructions - (void *)_start + xenmap; > - region.end = (void *)__alt_instructions_end - (void *)_start + > xenmap; > - > - ret = __apply_alternatives(®ion); > + ret = __apply_alternatives(®ion, xenmap - (void *)_start); > /* The patching is not expected to fail during boot. */ > BUG_ON(ret != 0); > > - unregister_virtual_region(&patch_region); > - > vunmap(xenmap); > > /* Barriers provided by the cache flushing */ > @@ -235,7 +219,7 @@ int apply_alternatives(const struct alt_instr *start, > const struct alt_instr *en > .end = end, > }; > > - return __apply_alternatives(®ion); > + return __apply_alternatives(®ion, 0); > } > > /* > -- > 2.11.0 > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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