On 09/21/2016 06:32 PM, Konrad Rzeszutek Wilk wrote:
Certain platforms, such as ARM [32|64] add extra mapping symbols such as $x (for ARM64 instructions), or more interesting to this patch: $t (for Thumb instructions). These symbols are suppose to help the final linker to make any adjustments (such as add an veneer). But more importantly - we do not compile Xen with any Thumb instructions (which are variable length) - and if we find these mapping symbols we should disallow such payload.Signed-off-by: Konrad Rzeszutek Wilk <konrad.w...@oracle.com> --- Cc: Konrad Rzeszutek Wilk <konrad.w...@oracle.com> Cc: Ross Lagerwall <ross.lagerw...@citrix.com> Cc: Stefano Stabellini <sstabell...@kernel.org> Cc: Julien Grall <julien.gr...@arm.com Cc: Jan Beulich <jbeul...@suse.com> Cc: Andrew Cooper <andrew.coop...@citrix.com> v3: New submission. Use &sym[i] instead of sym (as that will always be NULL). v4: Use bool instead of int for return Update comment in common code about ARM odd symbols. s/_check/_deny/ to make it more clear. v5: Also check for $t.* wildcard. Use Julien's variant where we roll the [2] check in the return. --- xen/arch/arm/livepatch.c | 16 ++++++++++++++++ xen/arch/x86/livepatch.c | 7 +++++++ xen/common/livepatch_elf.c | 7 +++++++ xen/include/xen/livepatch.h | 2 ++ 4 files changed, 32 insertions(+) diff --git a/xen/arch/arm/livepatch.c b/xen/arch/arm/livepatch.c index 9959315..5a99ab5 100644 --- a/xen/arch/arm/livepatch.c +++ b/xen/arch/arm/livepatch.c @@ -117,6 +117,22 @@ bool arch_livepatch_symbol_ok(const struct livepatch_elf *elf, return true; } +bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf, + const struct livepatch_elf_sym *sym) +{ +#ifdef CONFIG_ARM_32 + /* + * Xen does not use Thumb instructions - and we should not see any of + * them. If we do, abort. + */ + if ( sym->name && sym->name[0] == '$' && sym->name[1] == 't' ) + { + return ( !sym->name[2] || sym->name[2] == '.' ); + } +#endif + return false; +} + int arch_livepatch_perform_rel(struct livepatch_elf *elf, const struct livepatch_elf_sec *base, const struct livepatch_elf_sec *rela) diff --git a/xen/arch/x86/livepatch.c b/xen/arch/x86/livepatch.c index 7a369a0..9663ef6 100644 --- a/xen/arch/x86/livepatch.c +++ b/xen/arch/x86/livepatch.c @@ -131,6 +131,13 @@ bool arch_livepatch_symbol_ok(const struct livepatch_elf *elf, return true; } +bool arch_livepatch_symbol_deny(const struct livepatch_elf *elf, + const struct livepatch_elf_sym *sym) +{ + /* No special checks on x86. */ + return false; +} + int arch_livepatch_perform_rel(struct livepatch_elf *elf, const struct livepatch_elf_sec *base, const struct livepatch_elf_sec *rela) diff --git a/xen/common/livepatch_elf.c b/xen/common/livepatch_elf.c index f46990e..ec74beb 100644 --- a/xen/common/livepatch_elf.c +++ b/xen/common/livepatch_elf.c @@ -251,6 +251,13 @@ static int elf_get_sym(struct livepatch_elf *elf, const void *data) sym[i].sym = s; sym[i].name = strtab_sec->data + delta; + /* e.g. On ARM we should NEVER see $t* symbols. */
I'd prefer this comment in ARM's arch_livepatch_symbol_deny. Either way, Reviewed-by: Ross Lagerwall <ross.lagerw...@citrix.com> _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel
