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.
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)
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
--
2.25.1On 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/
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