x86/rdrand: Disable RDSEED on AMD Cyan Skillfish

AMD Cyan Skillfish (Family 17h, Model 47h, Stepping 0h) has an error that
causes RDSEED to always return 0xffffffff, while RDRAND works correctly.

Mask the RDSEED cap for this CPU so that both /proc/cpuinfo and direct CPUID
read report RDSEED as unavailable.

  [ bp: Move to amd.c, massage. ]

Signed-off-by: Mikhail Paulyshka <me@mixaill.net>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/20250524145319.209075-1-me@mixaill.net

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index b7dded3c811328fae3fbfa2dc43ecceb212f2519..5cfb5d74dd5f58b367497877a462a8a84439780e 100644 (file)
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -628,6 +628,7 @@
 #define MSR_AMD64_OSVW_STATUS          0xc0010141
 #define MSR_AMD_PPIN_CTL               0xc00102f0
 #define MSR_AMD_PPIN                   0xc00102f1
+#define MSR_AMD64_CPUID_FN_7           0xc0011002
 #define MSR_AMD64_CPUID_FN_1           0xc0011004
 #define MSR_AMD64_LS_CFG               0xc0011020
 #define MSR_AMD64_DC_CFG               0xc0011022

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 655f44f89dedb32396c6d090167750ef781131bd..e1c4661f443012cb8415e0fd6d26519224d0c67f 100644 (file)
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -930,6 +930,13 @@ static void init_amd_zen2(struct cpuinfo_x86 *c)
        init_spectral_chicken(c);
        fix_erratum_1386(c);
        zen2_zenbleed_check(c);
+
+       /* Disable RDSEED on AMD Cyan Skillfish because of an error. */
+       if (c->x86_model == 0x47 && c->x86_stepping == 0x0) {
+               clear_cpu_cap(c, X86_FEATURE_RDSEED);
+               msr_clear_bit(MSR_AMD64_CPUID_FN_7, 18);
+               pr_emerg("RDSEED is not reliable on this platform; disabling.\n");
+       }
 }
 
 static void init_amd_zen3(struct cpuinfo_x86 *c)

diff --git a/tools/arch/x86/include/asm/msr-index.h b/tools/arch/x86/include/asm/msr-index.h
index b7dded3c811328fae3fbfa2dc43ecceb212f2519..5cfb5d74dd5f58b367497877a462a8a84439780e 100644 (file)
--- a/tools/arch/x86/include/asm/msr-index.h
+++ b/tools/arch/x86/include/asm/msr-index.h
@@ -628,6 +628,7 @@
 #define MSR_AMD64_OSVW_STATUS          0xc0010141
 #define MSR_AMD_PPIN_CTL               0xc00102f0
 #define MSR_AMD_PPIN                   0xc00102f1
+#define MSR_AMD64_CPUID_FN_7           0xc0011002
 #define MSR_AMD64_CPUID_FN_1           0xc0011004
 #define MSR_AMD64_LS_CFG               0xc0011020
 #define MSR_AMD64_DC_CFG               0xc0011022