[PATCH] x86/sev: Fix position dependent variable references in startup code
Ard Biesheuvel
ardb+git at google.com
Sat Feb 3 04:53:06 PST 2024
From: Ard Biesheuvel <ardb at kernel.org>
The early startup code executes from a 1:1 mapping of memory, which
differs from the mapping that the code was linked and/or relocated to
run at. The latter mapping is not active yet at this point, and so
symbol references that rely on it will fault. Given that the core kernel
is built without -fPIC, symbol references are typically emitted as
absolute, and so any such references occuring in the early startup code
will therefore crash the kernel.
While an attempt was made to work around this for the early SEV/SME
startup code, by forcing RIP-relative addressing for certain global
SEV/SME variables via inline assembly (see snp_cpuid_get_table() for
example), RIP-relative addressing must be pervasively enforced for
SEV/SME global variables when accessed prior to page table fixups.
__startup_64() already handles this issue for select non-SEV/SME global
variables using fixup_pointer(), which adjusts the pointer relative to a
`physaddr` argument. To avoid having to pass around this `physaddr`
argument across all functions needing to apply pointer fixups, this
patch introduces the macro RIP_RELATIVE_REF(), which generates a
RIP-relative reference to a given global variable. The macro is used
where necessary to force RIP-relative accesses to global variables.
For backporting purposes, this patch makes no attempt at cleaning up
other occurrences of this pattern, involving either inline asm or
fixup_pointer(). Those will be addressed by subsequent patches.
Link: https://lore.kernel.org/all/20240130220845.1978329-1-kevinloughlin@google.com/
Co-developed-by: Kevin Loughlin <kevinloughlin at google.com>
Signed-off-by: Kevin Loughlin <kevinloughlin at google.com>
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
arch/x86/coco/core.c | 7 +----
arch/x86/include/asm/asm.h | 13 ++++++++++
arch/x86/include/asm/coco.h | 8 +++++-
arch/x86/include/asm/mem_encrypt.h | 13 ++++++----
arch/x86/kernel/sev-shared.c | 12 ++++-----
arch/x86/kernel/sev.c | 4 +--
arch/x86/mm/mem_encrypt_identity.c | 27 +++++++++-----------
7 files changed, 49 insertions(+), 35 deletions(-)
diff --git a/arch/x86/coco/core.c b/arch/x86/coco/core.c
index eeec9986570e..d07be9d05cd0 100644
--- a/arch/x86/coco/core.c
+++ b/arch/x86/coco/core.c
@@ -14,7 +14,7 @@
#include <asm/processor.h>
enum cc_vendor cc_vendor __ro_after_init = CC_VENDOR_NONE;
-static u64 cc_mask __ro_after_init;
+u64 cc_mask __ro_after_init;
static bool noinstr intel_cc_platform_has(enum cc_attr attr)
{
@@ -148,8 +148,3 @@ u64 cc_mkdec(u64 val)
}
}
EXPORT_SYMBOL_GPL(cc_mkdec);
-
-__init void cc_set_mask(u64 mask)
-{
- cc_mask = mask;
-}
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index fbcfec4dc4cc..41b408b3dfb6 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -113,6 +113,19 @@
#endif
+#ifndef __ASSEMBLY__
+#ifndef __pic__
+static inline __pure void *rip_relative_ptr(void *p)
+{
+ asm("leaq %c1(%%rip), %0" : "=r"(p) : "i"(p));
+ return p;
+}
+#define RIP_RELATIVE_REF(var) (*(typeof(&(var)))rip_relative_ptr(&(var)))
+#else
+#define RIP_RELATIVE_REF(var) (var)
+#endif
+#endif
+
/*
* Macros to generate condition code outputs from inline assembly,
* The output operand must be type "bool".
diff --git a/arch/x86/include/asm/coco.h b/arch/x86/include/asm/coco.h
index 6ae2d16a7613..d6865e0f7587 100644
--- a/arch/x86/include/asm/coco.h
+++ b/arch/x86/include/asm/coco.h
@@ -2,6 +2,7 @@
#ifndef _ASM_X86_COCO_H
#define _ASM_X86_COCO_H
+#include <asm/asm.h>
#include <asm/types.h>
enum cc_vendor {
@@ -11,9 +12,14 @@ enum cc_vendor {
};
extern enum cc_vendor cc_vendor;
+extern u64 cc_mask;
#ifdef CONFIG_ARCH_HAS_CC_PLATFORM
-void cc_set_mask(u64 mask);
+static inline void cc_set_mask(u64 mask)
+{
+ RIP_RELATIVE_REF(cc_mask) = mask;
+}
+
u64 cc_mkenc(u64 val);
u64 cc_mkdec(u64 val);
#else
diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 359ada486fa9..1427b5fc416c 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -15,6 +15,7 @@
#include <linux/init.h>
#include <linux/cc_platform.h>
+#include <asm/asm.h>
#include <asm/bootparam.h>
#ifdef CONFIG_X86_MEM_ENCRYPT
@@ -58,6 +59,11 @@ void __init mem_encrypt_free_decrypted_mem(void);
void __init sev_es_init_vc_handling(void);
+static inline u64 sme_get_me_mask(void)
+{
+ return RIP_RELATIVE_REF(sme_me_mask);
+}
+
#define __bss_decrypted __section(".bss..decrypted")
#else /* !CONFIG_AMD_MEM_ENCRYPT */
@@ -89,6 +95,8 @@ early_set_mem_enc_dec_hypercall(unsigned long vaddr, unsigned long size, bool en
static inline void mem_encrypt_free_decrypted_mem(void) { }
+static inline u64 sme_get_me_mask(void) { return 0; }
+
#define __bss_decrypted
#endif /* CONFIG_AMD_MEM_ENCRYPT */
@@ -106,11 +114,6 @@ void add_encrypt_protection_map(void);
extern char __start_bss_decrypted[], __end_bss_decrypted[], __start_bss_decrypted_unused[];
-static inline u64 sme_get_me_mask(void)
-{
- return sme_me_mask;
-}
-
#endif /* __ASSEMBLY__ */
#endif /* __X86_MEM_ENCRYPT_H__ */
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 5db24d0fc557..df3a89cbca46 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -560,9 +560,9 @@ static int snp_cpuid(struct ghcb *ghcb, struct es_em_ctxt *ctxt, struct cpuid_le
leaf->eax = leaf->ebx = leaf->ecx = leaf->edx = 0;
/* Skip post-processing for out-of-range zero leafs. */
- if (!(leaf->fn <= cpuid_std_range_max ||
- (leaf->fn >= 0x40000000 && leaf->fn <= cpuid_hyp_range_max) ||
- (leaf->fn >= 0x80000000 && leaf->fn <= cpuid_ext_range_max)))
+ if (!(leaf->fn <= RIP_RELATIVE_REF(cpuid_std_range_max) ||
+ (leaf->fn >= 0x40000000 && leaf->fn <= RIP_RELATIVE_REF(cpuid_hyp_range_max)) ||
+ (leaf->fn >= 0x80000000 && leaf->fn <= RIP_RELATIVE_REF(cpuid_ext_range_max))))
return 0;
}
@@ -1072,11 +1072,11 @@ static void __init setup_cpuid_table(const struct cc_blob_sev_info *cc_info)
const struct snp_cpuid_fn *fn = &cpuid_table->fn[i];
if (fn->eax_in == 0x0)
- cpuid_std_range_max = fn->eax;
+ RIP_RELATIVE_REF(cpuid_std_range_max) = fn->eax;
else if (fn->eax_in == 0x40000000)
- cpuid_hyp_range_max = fn->eax;
+ RIP_RELATIVE_REF(cpuid_hyp_range_max) = fn->eax;
else if (fn->eax_in == 0x80000000)
- cpuid_ext_range_max = fn->eax;
+ RIP_RELATIVE_REF(cpuid_ext_range_max) = fn->eax;
}
}
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 002af6c30601..1cf348e19556 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -748,7 +748,7 @@ void __init early_snp_set_memory_private(unsigned long vaddr, unsigned long padd
* This eliminates worries about jump tables or checking boot_cpu_data
* in the cc_platform_has() function.
*/
- if (!(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
+ if (!(RIP_RELATIVE_REF(sev_status) & MSR_AMD64_SEV_SNP_ENABLED))
return;
/*
@@ -767,7 +767,7 @@ void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr
* This eliminates worries about jump tables or checking boot_cpu_data
* in the cc_platform_has() function.
*/
- if (!(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
+ if (!(RIP_RELATIVE_REF(sev_status) & MSR_AMD64_SEV_SNP_ENABLED))
return;
/* Ask hypervisor to mark the memory pages shared in the RMP table. */
diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index efe9f217fcf9..d8d14133b654 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -304,7 +304,8 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
* instrumentation or checking boot_cpu_data in the cc_platform_has()
* function.
*/
- if (!sme_get_me_mask() || sev_status & MSR_AMD64_SEV_ENABLED)
+ if (!sme_get_me_mask() ||
+ RIP_RELATIVE_REF(sev_status) & MSR_AMD64_SEV_ENABLED)
return;
/*
@@ -541,11 +542,11 @@ void __init sme_enable(struct boot_params *bp)
me_mask = 1UL << (ebx & 0x3f);
/* Check the SEV MSR whether SEV or SME is enabled */
- sev_status = __rdmsr(MSR_AMD64_SEV);
- feature_mask = (sev_status & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
+ RIP_RELATIVE_REF(sev_status) = msr = __rdmsr(MSR_AMD64_SEV);
+ feature_mask = (msr & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
/* The SEV-SNP CC blob should never be present unless SEV-SNP is enabled. */
- if (snp && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
+ if (snp && !(msr & MSR_AMD64_SEV_SNP_ENABLED))
snp_abort();
/* Check if memory encryption is enabled */
@@ -571,7 +572,6 @@ void __init sme_enable(struct boot_params *bp)
return;
} else {
/* SEV state cannot be controlled by a command line option */
- sme_me_mask = me_mask;
goto out;
}
@@ -590,16 +590,13 @@ void __init sme_enable(struct boot_params *bp)
cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr |
((u64)bp->ext_cmd_line_ptr << 32));
- if (cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer)) < 0)
- goto out;
-
- if (!strncmp(buffer, cmdline_on, sizeof(buffer)))
- sme_me_mask = me_mask;
+ if (cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer)) < 0 ||
+ strncmp(buffer, cmdline_on, sizeof(buffer)))
+ return;
out:
- if (sme_me_mask) {
- physical_mask &= ~sme_me_mask;
- cc_vendor = CC_VENDOR_AMD;
- cc_set_mask(sme_me_mask);
- }
+ RIP_RELATIVE_REF(sme_me_mask) = me_mask;
+ physical_mask &= ~me_mask;
+ cc_vendor = CC_VENDOR_AMD;
+ cc_set_mask(me_mask);
}
base-commit: f9e6f00d93d34f60f90b42c24e80194b11a72bb2
--
2.43.0.594.gd9cf4e227d-goog
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