| Message ID | 20230819094332.8535-3-jo.vanbulck@cs.kuleuven.be (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | selftests/sgx: Fix compilation errors | expand |
On Sat, 2023-08-19 at 11:43 +0200, Jo Van Bulck wrote: > The current combination of -static and -fPIC creates a static executable > with position-dependent addresses for global variables. Use -static-pie > and -fPIE to create a proper static position independent executable that > can be loaded at any address without a dynamic linker. IMHO, this patch is also mixing different things together. Specifically, ... > > Link: https://lore.kernel.org/all/f9c24d89-ed72-7d9e-c650-050d722c6b04@cs.kuleuven.be/ > Signed-off-by: Jo Van Bulck <jo.vanbulck@cs.kuleuven.be> > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> > --- > tools/testing/selftests/sgx/Makefile | 2 +- > tools/testing/selftests/sgx/test_encl.lds | 1 + > tools/testing/selftests/sgx/test_encl_bootstrap.S | 12 ++++++------ > 3 files changed, 8 insertions(+), 7 deletions(-) > > diff --git a/tools/testing/selftests/sgx/Makefile b/tools/testing/selftests/sgx/Makefile > index 50aab6b57..1d6315a2e 100644 > --- a/tools/testing/selftests/sgx/Makefile > +++ b/tools/testing/selftests/sgx/Makefile > @@ -13,7 +13,7 @@ endif > > INCLUDES := -I$(top_srcdir)/tools/include > HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC -z noexecstack > -ENCL_CFLAGS := -Wall -Werror -static -nostdlib -nostartfiles -fPIC \ > +ENCL_CFLAGS := -Wall -Werror -static-pie -nostdlib -nostartfiles -fPIE \ > -fno-stack-protector -mrdrnd $(INCLUDES) ... I think only this build flag change should be done in this patch, as described in the changelog. Because ... > > TEST_CUSTOM_PROGS := $(OUTPUT)/test_sgx > diff --git a/tools/testing/selftests/sgx/test_encl.lds b/tools/testing/selftests/sgx/test_encl.lds > index a1ec64f7d..62d37160f 100644 > --- a/tools/testing/selftests/sgx/test_encl.lds > +++ b/tools/testing/selftests/sgx/test_encl.lds > @@ -10,6 +10,7 @@ PHDRS > SECTIONS > { > . = 0; > + __encl_base = .; > .tcs : { > *(.tcs*) > } : tcs > diff --git a/tools/testing/selftests/sgx/test_encl_bootstrap.S b/tools/testing/selftests/sgx/test_encl_bootstrap.S > index 03ae0f57e..28fe5d2ac 100644 > --- a/tools/testing/selftests/sgx/test_encl_bootstrap.S > +++ b/tools/testing/selftests/sgx/test_encl_bootstrap.S > @@ -42,9 +42,12 @@ > encl_entry: > # RBX contains the base address for TCS, which is the first address > # inside the enclave for TCS #1 and one page into the enclave for > - # TCS #2. By adding the value of encl_stack to it, we get > - # the absolute address for the stack. > - lea (encl_stack)(%rbx), %rax > + # TCS #2. First make it relative by substracting __encl_base and > + # then add the address of encl_stack to get the address for the stack. > + lea __encl_base(%rip), %rax > + sub %rax, %rbx > + lea encl_stack(%rip), %rax > + add %rbx, %rax ... if I am not missing anything, this chunk isn't needed for _this_ patch. The old code can still produce the correct stack address. __encl_base is only needed for the next patch, thus the relevant change should be moved to the next patch. > jmp encl_entry_core > encl_dyn_entry: > # Entry point for dynamically created TCS page expected to follow > @@ -55,12 +58,9 @@ encl_entry_core: > push %rax > > push %rcx # push the address after EENTER > - push %rbx # push the enclave base address > > call encl_body > > - pop %rbx # pop the enclave base address > - > /* Clear volatile GPRs, except RAX (EEXIT function). */ > xor %rcx, %rcx > xor %rdx, %rdx I honestly don't understand what's the purpose of this code change. I believe this change can be done (because it looks there's no need push/pop %rbx in the first place), but again it should be in the next patch I suppose.
On 22.08.23 02:26, Huang, Kai wrote: > ... I think only this build flag change should be done in this patch, as > described in the changelog. > > Because ... > ... if I am not missing anything, this chunk isn't needed for _this_ patch. The > old code can still produce the correct stack address. __encl_base is only needed > for the next patch, thus the relevant change should be moved to the next patch. I understand the confusion, but the reason I included this small change already in this commit is to make sure the commit compiles standalone. That is, when building the original assembly statement "lea (encl_stack)(%rbx), %rax" with -static-pie -fPIE, the linker complains about a relocation it cannot resolve: /usr/local/bin/ld: /tmp/cchIWyfG.o: relocation R_X86_64_32S against `.data' can not be used when making a PIE object; recompile with -fPIE collect2: error: ld returned 1 exit status The problem is that only RIP-relative addressing is legit for local symbols, ie "encl_stack(%rip)". Hence, __encl_base is already needed here to calculate the stack address in the updated asm sequence in this patch. Hope this helps clarifying! > I honestly don't understand what's the purpose of this code change. I believe > this change can be done (because it looks there's no need push/pop %rbx in the > first place), but again it should be in the next patch I suppose. Thanks, the purpose indeed was merely to remove redundant code that is not needed. I see that it would be better to include this in a separate patch, so I'll update this in the next patch revision. FWIW: if this is okay, while I'm on it, I'll also take a shot at removing remaining (unnecessary) assembly register cleansing code to make it more obvious that the test enclave is *not* exemplary secure, as per our earlier discussions. Ie in response to Dave's earlier comments that "The only patches I want for the kernel are to make the test enclave more *obviously* insecure." [1]. Best, Jo [1] https://lore.kernel.org/all/da0cfb1e-e347-f7f2-ac72-aec0ee0d867d@intel.com/
diff --git a/tools/testing/selftests/sgx/Makefile b/tools/testing/selftests/sgx/Makefile index 50aab6b57..1d6315a2e 100644 --- a/tools/testing/selftests/sgx/Makefile +++ b/tools/testing/selftests/sgx/Makefile @@ -13,7 +13,7 @@ endif INCLUDES := -I$(top_srcdir)/tools/include HOST_CFLAGS := -Wall -Werror -g $(INCLUDES) -fPIC -z noexecstack -ENCL_CFLAGS := -Wall -Werror -static -nostdlib -nostartfiles -fPIC \ +ENCL_CFLAGS := -Wall -Werror -static-pie -nostdlib -nostartfiles -fPIE \ -fno-stack-protector -mrdrnd $(INCLUDES) TEST_CUSTOM_PROGS := $(OUTPUT)/test_sgx diff --git a/tools/testing/selftests/sgx/test_encl.lds b/tools/testing/selftests/sgx/test_encl.lds index a1ec64f7d..62d37160f 100644 --- a/tools/testing/selftests/sgx/test_encl.lds +++ b/tools/testing/selftests/sgx/test_encl.lds @@ -10,6 +10,7 @@ PHDRS SECTIONS { . = 0; + __encl_base = .; .tcs : { *(.tcs*) } : tcs diff --git a/tools/testing/selftests/sgx/test_encl_bootstrap.S b/tools/testing/selftests/sgx/test_encl_bootstrap.S index 03ae0f57e..28fe5d2ac 100644 --- a/tools/testing/selftests/sgx/test_encl_bootstrap.S +++ b/tools/testing/selftests/sgx/test_encl_bootstrap.S @@ -42,9 +42,12 @@ encl_entry: # RBX contains the base address for TCS, which is the first address # inside the enclave for TCS #1 and one page into the enclave for - # TCS #2. By adding the value of encl_stack to it, we get - # the absolute address for the stack. - lea (encl_stack)(%rbx), %rax + # TCS #2. First make it relative by substracting __encl_base and + # then add the address of encl_stack to get the address for the stack. + lea __encl_base(%rip), %rax + sub %rax, %rbx + lea encl_stack(%rip), %rax + add %rbx, %rax jmp encl_entry_core encl_dyn_entry: # Entry point for dynamically created TCS page expected to follow @@ -55,12 +58,9 @@ encl_entry_core: push %rax push %rcx # push the address after EENTER - push %rbx # push the enclave base address call encl_body - pop %rbx # pop the enclave base address - /* Clear volatile GPRs, except RAX (EEXIT function). */ xor %rcx, %rcx xor %rdx, %rdx